[Dragonshadow]

Using SM 1.3 its really easy.

PHP Code:

public Action:OnPlayerRunCmd(client, &buttons, &impulse, Float:vel[3], Float:angles[3], &weapon)
{
    if(IsClientInGame(client) && IsPlayerAlive(client) && GetClientTeam(client) == 3 && weapon > 0)
    {
        new melee = GetPlayerWeaponSlot(client, 2);
        if (melee > -1 && weapon != melee)
        {
            weapon = melee;
        }
    }
}