When our son was having hitting issues at daycare (trying to fit in/engage with the older boys when they joined his 3s class on the playground), our primary response was to let him know we were checking up on him and that we absolutely did not approve of hitting other people. Every day at drop off, we reviewed our expectations - no hitting. And every day when we picked him up, we made sure he saw us asking his teacher how the day went - was there any hitting? That later transitioned to (merely) asking DS ourselves if there was no hitting? And if we asked his teacher, would she say the same thing?
We *did* somewhat restrict TV, because he had started watching old Spiderman clips from Electric Company. While they seemed benign on the surface (no fighting visualized; action was simulated in comic book form), we decided they correlated too closely in time to the daycare hitting to continue them. So, we told him, "no more spiderman" and we let him know it was because he was hitting. He was also hitting during roughhousing with DH and couldn't seem to learn the "rules" about roughhousing, so we stopped the roughhousing game, again, letting him know that it was connected to his inability to control his body.