Given that Oliver seems to be alone in the shower room, I’m guessing there was some dealing with the prison guards for the bad guy to get the jump on Oliver.
Can’t a guy take a prison shower in peace without being jumped by another prisoner?
It would make sense if both the guards and the other prisoners had it out for Oliver, unfortunately.
We obviously don’t have the context for this throwdown (courtesy of the Arrow Twitter account) just yet, but it doesn’t look like much of a fair fight.