diff --git a/src/client/MultiTabDetector.ts b/src/client/MultiTabDetector.ts
new file mode 100644
index 000000000..bd9db4c5f
--- /dev/null
+++ b/src/client/MultiTabDetector.ts
@@ -0,0 +1,130 @@
+export class MultiTabDetector {
+  private focusChanges: number[] = [];
+  private readonly maxFocusChanges: number = 10;
+  private readonly timeWindow: number = 60_000;
+  private readonly punishmentDelays: number[] = [
+    2_000, 3_000, 5_000, 10_000, 30_000, 60_000,
+  ];
+  private lastFocusChangeTime: number = 0;
+  private isPunished: boolean = false;
+  private isMonitoring: boolean = false;
+  private startPenaltyCallback?: (duration: number) => void;
+
+  private numPunishmentsGiven = 0;
+
+  /**
+   * Start monitoring for multi-tabbing behavior
+   *
+   * @param startPenalty Callback function when punishment starts
+   */
+  public startMonitoring(startPenalty: (duration: number) => void): void {
+    if (this.isMonitoring) return;
+
+    this.isMonitoring = true;
+    this.startPenaltyCallback = startPenalty;
+
+    // Event listeners for window focus/blur
+    window.addEventListener("blur", this.handleFocusChange.bind(this));
+    window.addEventListener("focus", this.handleFocusChange.bind(this));
+
+    // Also track visibility changes for tab switching
+    document.addEventListener(
+      "visibilitychange",
+      this.handleVisibilityChange.bind(this),
+    );
+  }
+
+  public stopMonitoring(): void {
+    if (!this.isMonitoring) return;
+
+    this.isMonitoring = false;
+
+    // Remove event listeners
+    window.removeEventListener("blur", this.handleFocusChange.bind(this));
+    window.removeEventListener("focus", this.handleFocusChange.bind(this));
+    document.removeEventListener(
+      "visibilitychange",
+      this.handleVisibilityChange.bind(this),
+    );
+
+    // Clear data
+    this.focusChanges = [];
+    this.isPunished = false;
+  }
+
+  private handleFocusChange(): void {
+    const currentTime = Date.now();
+
+    this.recordFocusChange(currentTime);
+
+    // Check for multi-tabbing when focus is gained
+    if (document.hasFocus() && !this.isPunished) {
+      this.checkForMultiTabbing(currentTime);
+    }
+  }
+
+  private handleVisibilityChange(): void {
+    const currentTime = Date.now();
+
+    // Record and check regardless of current focus state
+    this.recordFocusChange(currentTime);
+
+    // Only check when tab becomes visible
+    if (document.visibilityState === "visible" && !this.isPunished) {
+      this.checkForMultiTabbing(currentTime);
+    }
+  }
+
+  private recordFocusChange(timestamp: number): void {
+    if (Math.abs(this.lastFocusChangeTime - timestamp) < 100) {
+      // Don't count multiple triggers at same time
+      return;
+    }
+    this.focusChanges.push(timestamp);
+    console.log(`pushing focus change at ${timestamp}`);
+    this.lastFocusChangeTime = timestamp;
+
+    // Keep only recent changes
+    if (this.focusChanges.length > this.maxFocusChanges) {
+      this.focusChanges.shift();
+    }
+  }
+
+  private checkForMultiTabbing(currentTime: number): void {
+    // Only if we have enough data points
+    if (this.focusChanges.length >= this.maxFocusChanges) {
+      const oldestChange = this.focusChanges[0];
+      const timeSpan = currentTime - oldestChange;
+
+      // If changes happened within detection window
+      if (timeSpan <= this.timeWindow) {
+        this.applyPunishment();
+      }
+    }
+  }
+
+  private applyPunishment(): void {
+    // Prevent multiple punishments
+    if (this.isPunished) return;
+    this.isPunished = true;
+
+    let punishmentDelay = 0;
+    if (this.numPunishmentsGiven >= this.punishmentDelays.length) {
+      punishmentDelay = this.punishmentDelays[this.punishmentDelays.length - 1];
+    } else {
+      punishmentDelay = this.punishmentDelays[this.numPunishmentsGiven];
+    }
+
+    this.numPunishmentsGiven++;
+
+    // Call the start penalty callback
+    if (this.startPenaltyCallback) {
+      this.startPenaltyCallback(punishmentDelay);
+    }
+
+    // Remove penalty after delay
+    setTimeout(() => {
+      this.isPunished = false;
+    }, punishmentDelay);
+  }
+}
diff --git a/src/client/graphics/GameRenderer.ts b/src/client/graphics/GameRenderer.ts
index 1fe89a791..9c92a3d0e 100644
--- a/src/client/graphics/GameRenderer.ts
+++ b/src/client/graphics/GameRenderer.ts
@@ -12,6 +12,7 @@ import { EmojiTable } from "./layers/EmojiTable";
 import { EventsDisplay } from "./layers/EventsDisplay";
 import { Layer } from "./layers/Layer";
 import { Leaderboard } from "./layers/Leaderboard";
+import { MultiTabModal } from "./layers/MultiTabModal";
 import { NameLayer } from "./layers/NameLayer";
 import { OptionsMenu } from "./layers/OptionsMenu";
 import { PlayerInfoOverlay } from "./layers/PlayerInfoOverlay";
@@ -125,6 +126,14 @@ export function createRenderer(
   playerPanel.eventBus = eventBus;
   playerPanel.emojiTable = emojiTable;
 
+  const multiTabModal = document.querySelector(
+    "multi-tab-modal",
+  ) as MultiTabModal;
+  if (!(multiTabModal instanceof MultiTabModal)) {
+    console.error("multi-tab modal not found");
+  }
+  multiTabModal.game = game;
+
   const layers: Layer[] = [
     new TerrainLayer(game, transformHandler),
     new TerritoryLayer(game, eventBus),
@@ -153,6 +162,7 @@ export function createRenderer(
     optionsMenu,
     topBar,
     playerPanel,
+    multiTabModal,
   ];
 
   return new GameRenderer(
diff --git a/src/client/graphics/layers/MultiTabModal.ts b/src/client/graphics/layers/MultiTabModal.ts
new file mode 100644
index 000000000..6855cfbda
--- /dev/null
+++ b/src/client/graphics/layers/MultiTabModal.ts
@@ -0,0 +1,131 @@
+import { LitElement, html } from "lit";
+import { customElement, property, state } from "lit/decorators.js";
+import { GameType } from "../../../core/game/Game";
+import { GameView } from "../../../core/game/GameView";
+import { MultiTabDetector } from "../../MultiTabDetector";
+import { translateText } from "../../Utils";
+import { Layer } from "./Layer";
+
+@customElement("multi-tab-modal")
+export class MultiTabModal extends LitElement implements Layer {
+  public game: GameView;
+
+  private detector: MultiTabDetector;
+
+  @property({ type: Number }) duration: number = 5000;
+  @state() private countdown: number = 5;
+  @state() private isVisible: boolean = false;
+
+  private intervalId?: number;
+
+  // Disable shadow DOM to allow Tailwind classes to work
+  createRenderRoot() {
+    return this;
+  }
+
+  tick() {
+    if (
+      this.game.inSpawnPhase() ||
+      this.game.config().gameConfig().gameType == GameType.Singleplayer
+    ) {
+      return;
+    }
+    if (!this.detector) {
+      this.detector = new MultiTabDetector();
+      this.detector.startMonitoring((duration: number) => {
+        this.show(duration);
+      });
+    }
+  }
+
+  // Show the modal with penalty information
+  public show(duration: number): void {
+    if (!this.game.myPlayer()?.isAlive()) {
+      return;
+    }
+    this.duration = duration;
+    this.countdown = Math.ceil(duration / 1000);
+    this.isVisible = true;
+
+    // Start countdown timer
+    this.intervalId = window.setInterval(() => {
+      this.countdown--;
+
+      if (this.countdown <= 0) {
+        this.hide();
+      }
+    }, 1000);
+
+    this.requestUpdate();
+  }
+
+  // Hide the modal
+  public hide(): void {
+    this.isVisible = false;
+
+    if (this.intervalId) {
+      window.clearInterval(this.intervalId);
+      this.intervalId = undefined;
+    }
+
+    // Dispatch event when modal is closed
+    this.dispatchEvent(
+      new CustomEvent("penalty-complete", {
+        bubbles: true,
+        composed: true,
+      }),
+    );
+
+    this.requestUpdate();
+  }
+
+  disconnectedCallback() {
+    super.disconnectedCallback();
+    if (this.intervalId) {
+      window.clearInterval(this.intervalId);
+    }
+  }
+
+  render() {
+    if (!this.isVisible) {
+      return html``;
+    }
+
+    return html`
+      <div
+        class="fixed inset-0 z-50 overflow-auto bg-red-500/20 flex items-center justify-center"
+      >
+        <div
+          class="relative p-6 bg-white dark:bg-gray-800 rounded-xl shadow-xl max-w-md w-full m-4 transition-all transform"
+        >
+          <h2 class="text-2xl font-bold mb-4 text-red-600 dark:text-red-400">
+            ${translateText("multi_tab.warning")}
+          </h2>
+
+          <p class="mb-4 text-gray-800 dark:text-gray-200">
+            ${translateText("multi_tab.detected")}
+          </p>
+
+          <p class="mb-4 text-gray-800 dark:text-gray-200">
+            ${translateText("multi_tab.please_wait")}
+            <span class="font-bold text-xl">${this.countdown}</span>
+            ${translateText("multi_tab.seconds")}
+          </p>
+
+          <div
+            class="w-full bg-gray-200 dark:bg-gray-700 rounded-full h-2.5 mb-4"
+          >
+            <div
+              class="bg-red-600 dark:bg-red-500 h-2.5 rounded-full transition-all duration-1000 ease-linear"
+              style="width: ${(this.countdown / (this.duration / 1000)) * 100}%"
+            ></div>
+          </div>
+
+          <p class="text-sm text-gray-600 dark:text-gray-400">
+            ${translateText("multi_tab.explanation")}
+          </p>
+        </div>
+      </div>
+    `;
+  }
+}
diff --git a/src/client/index.html b/src/client/index.html
index 78172b5fc..f0b8810f3 100644
--- a/src/client/index.html
+++ b/src/client/index.html
@@ -48,8 +48,10 @@
       .left-gutter-ad {
         position: fixed;
         left: 0;
-        top: 200px; /* Changed from top: 50% */
-        transform: none; /* Removed translateY(-50%) since we don't need to center anymore */
+        top: 200px;
+        /* Changed from top: 50% */
+        transform: none;
+        /* Removed translateY(-50%) since we don't need to center anymore */
         z-index: 40;
         width: 300px;
         height: 600px;
@@ -68,8 +70,10 @@
       .right-gutter-ad {
         position: fixed;
         right: 0;
-        top: 200px; /* Changed from top: 50% */
-        transform: none; /* Removed translateY(-50%) since we don't need to center anymore */
+        top: 200px;
+        /* Changed from top: 50% */
+        transform: none;
+        /* Removed translateY(-50%) since we don't need to center anymore */
         z-index: 40;
         width: 300px;
         height: 600px;
@@ -137,6 +141,7 @@
       gtag("config", "G-WQGQQ8RDN4");
     </script>
   </head>
+
   <body
     class="h-full select-none font-sans min-h-screen bg-opacity-0 bg-cover bg-center bg-fixed transition-opacity duration-300 ease-in-out flex flex-col"
   >
@@ -353,6 +358,7 @@
     <help-modal></help-modal>
     <dark-mode-button></dark-mode-button>
     <user-setting></user-setting>
+    <multi-tab-modal></multi-tab-modal>
     <div
       id="language-modal"
       class="fixed inset-0 bg-black bg-opacity-50 z-50 hidden flex justify-center items-center"