If there is any network disconnection or disruption during your PvP Arena battle, you're most likely seeing the "catch-up" replay, where it shows you what has happened so far in the battle as it tries to catch you up to the current, live round/turn.

 

You will not be able to enter commands, use character abilities, or cast Spells during this "catch-up" phase, as it is showing you what already happened.

 

The catch-up phase will end when it gets to the current turn, but if you backgrounded your app long enough or had a significantly long network disruption, the entire match may have already concluded, and you won't get control back before the match ends.