Please use the appropriate forum section for your threads. For questions about LFS, use the 
Technical Assistance sub-forum.
It's not possible to disqualify someone. The only way someone can be disqualified is when they don't serve a drive-through or stop&go penalty before finishing the race. You have some alternatives:
/p_dt USERNAME           : drive-through penalty
/p_sg USERNAME           : stop&go penalty
/setlap USERNAME Y       : set lap to 0 
/spec USERNAME           : spectate
/pitlane USERNAME        : send user to the pit lane
You can check all possible host admin commands here: 
https://en.lfsmanual.net/wiki/Commands#Host_commands