literally any action commited in the past is a paradox due to the butterfly effect, plus if you do some kind of action with significance then it'd alter your pre-travel condition to believe that action isn't necessary, causing you to not go back and cause a paradox
for example, go back in time and kill Riddler, then your current self wouldn't know anything about Riddler and wouldn't kill what is percieved as a random innocent german that disappeared/died under mysterious circumstances