[GoldNux]

Originally Posted by Natsheh My suggestion would be to kill the user before changing its team.

Thanks man, it works now!
This is what it looks like if anyone has the same issue:

PHP Code:

public SwapTeams()
{
    new players[32];
    new playercount;
    get_players(players, playercount, "h");
    
    new i, id
    for (i=0; i<playercount; i++)
    {
        id = players[i]
        new Float:flFrags
        pev(id, pev_frags, flFrags)
        set_pev(id, pev_frags, ++flFrags)

        dllfunc(DLLFunc_ClientKill, id)
        if (cs_get_user_team(id) != CS_TEAM_SPECTATOR && cs_get_user_team(id) != CS_TEAM_UNASSIGNED) // You also check if he hasn't chosen any team yet, ie "unassigned".
        {
            cs_set_user_team(id, (cs_get_user_team(id) == CS_TEAM_T) ? CS_TEAM_CT : CS_TEAM_T)
        }
    }
}