Even then, it's a fools errand. Assume you are able to access the opponents comm channels:

How do you relay that to the coaches?
Does someone on the sidelines have a comms channel waiting for the thumbs up from the hacker?
Are the coaches prepped to decipher the verbal calls from the other team?
How quickly can they turn that into actionable Intel and make the appropriate defensive selection?
Can they get the new call in to their defensive unit in time before the snap?

The logistical hurdles added by helmet comms are significant and it's a bad idea to try it.