I'm guessing you run an EntMod server and want to know if someone crashed the server by using a certain command. If that's the case, search for EntMod Manager.
Anyway, to see which command crashed the server, just log all commands executed that could possibly crash the server. That means writing the commands to a file, like a txt file as they are executed. Also, write a line in the file when the server starts. That way, you can see what the last command was before the server started, which is also the last command executed during the previous session. This last command is most likely the one that caused the crash.
client_PreThink cannot help you to find the command that caused the crash.