new
    MostKills,
    RoundKills[MAX_PLAYERRS];

public OnPlayerConnect(playerid)
{
    RoundKills[playerid] = 0;
    return 1;
}

public OnPlayerDeath(playerid, killerid, reason)
{
    RoundKills[killerid] ++;
    return 1;
}

// wherever the round ends

for(new i = 0; i < MAX_PLAYERS; i ++)
{
    if(!IsPlayerConnected(i)) continue;

    if(RoundKills[i] > MostKills)
    {
        MostKills = RoundKills[i];
    }

}

for(new i = 0; i < MAX_PLAYERS; i ++)
{
    if(!IsPlayerConnected(i)) continue;

    if(RoundKills[i] >= MostKills)
    {
        GetPlayerName(i, sendername, sizeof(sendername));
        format(string, sizeof(string),"%s has achieved the most kills.", sendername);
        SendClientMEssageToAll(COLOR_BLUE, string);
    }
    RoundKills[i] = 0;
}

MostKills = 0;