Rather self-explanatory.

For the average team this should happen once or twice a season. Lately i've gotten used to seeing this as much as twice a game.

Conversely, not sure if i've ever seen a punt return for 6, which does occasionally happen in professional leagues.

Punt returns used to be all the rage for non-stop TDs, however, that got shut down majorly.

When I started using overrides for my kickoff team, I stopped seeing this happen against me as often. But my experience may be just anecdotal.

Yes, fortify your gunners and it cuts back drastically on the returns. There's a trap with that but once you gain experience playing you see that the top rated gunners always aren't the best.