[Konstantinos]

Don't use PVars - they're slower.

pawn Код:

static
    Float: Player_DamageTaken[MAX_PLAYERS];

// OnPlayerConnect:
Player_DamageTaken[playerid] = 0.0;

// OnPlayerDeath:
Player_DamageTaken[playerid] = 0.0;

// OnPlayerTakeDamage (damage taken by players):
if (issuerid != INVALID_PLAYER_ID)
{
    Player_DamageTaken[playerid] += amount;
}

Player_DamageTaken[playerid] stores the total amount a player took damage by players. In each round (if you have of course) you can reset it to 0.