[Antithasys]

yes

new bool:IsArenaMode = false;
 
public OnPluginStart()
{
     TFGameModeArena = FindConVar("tf_gamemode_arena");
}
 
public OnMapStart()
{
     if (GetConVarInt(TFGameModeArena))
          IsArenaMode = true;
}

Then run a logic statement based upon IsArenaMode.

P.S. This works because the cvar is either a 1 or 0. If it's not in arena mode it's 0 or false, otherwise it's true.