// TOP OF SCRIPT
new chatcount[MAX_PLAYERS];

// Inside OnPlayerConnect
public OnPlayerConnect(playerid)
{
    SetTimerEx("antispam", 2000, 1, "i", playerid);
    // The rest of your code
    return 1;
}

// Somewhere
forward antispam(playerid);
public antispam(playerid)
{
    if(chatcount[playerid] > 3) // If player sent more than 3 messages in 2 seconds... probably a bot/keybind
    {
        return Kick(playerid); // Kick player if spamming, now you can do anything to him.
    }
    else
    {
        chatcount[playerid] = 0; // If he didn't spam, reset count.
    }
    return 1;
}

// In your chat, e.g. OnPlayerText
public OnPlayerText(playerid, text[])
{
    chatcount[playerid]++;
    // THE REST OF YOUR CODE
    return 1;
}

public OnPlayerText(playerid, text[])//This Callback is called as soon as a player types smth. into the chat.
{
    SpamCount[playerid]++;
    if(SpamCount[playerid] == 1)
    {
          spamtime[playerid][0] = gettime();
    }
    if(SpamCount[playerid] == 2) 
    {
        if(gettime()-spamtime[playerid][0] < 2)//We will check if the player send the next message within two seconds. And if yes give him a warning or something.
        {
            Give a warning.
            spamtime[playerid][1] = gettime();
        } else { SpamCount[playerid] = 0; }
    } 
     if(SpamCount[playerid] == 3) 
    {
        if(gettime()-spamtime[playerid][1] < 3)//We will check if the player send the next message within 3 seconds. And if yes give him a warning or something.
        {
            Kick him.
            SpamCount[playerid] = 0;
        } else { SpamCount[playerid] = 0; }
    }
}