The Guard Chief is a fairly flat character. He's a bossy prison guard, telling Alex to stand behind a white line. (Honestly, as far as prisons go, that's fairly tame.)
Although Alex is beaten by the police before going to jail, once he's in jail, it seems fairly cushy. He isn't attacked or hurt or mistreated in any way. He just has to…stand behind a line. Sometimes he has to stretch his arm to sign a document. This is far from prison brutality.
The Guard Chief mostly seems to be comic relief. But for a movie that seems to suggest that prison isn't good for criminals, having a guard who is practically a jester makes it seem like prison is a joke. Maybe Alex should have been smacked around a bit?