If I were the commissioner, there are a few things I would change in sports. I'll stick to the sports where most of my play by play experience is..

BASEBALL
The DH. Gone at all levels. 9 in the batting order, same nine in the field. The DH is a bad idea left over from 1970s, a decade noted for really bad ideas. I’m also no fan of courtesy runners in high school baseball and softball. If a pitcher or catcher is gassed after running the bases, some conditioning work is in order. It isn’t that far around the bases.

Bats not made of wood. Gone. If you can hit a little, you’re not going to break a lot of bats.

No more stepping out of the box after every pitch. I’ve seen enough obsessive fiddling with the Velcro on the batting gloves. Get in there and hit. Pace of play is an issue in baseball and this is a huge time waster.
Play with the Velcro on the bench. An exception is granted for fouling a ball off your body. There would be an exception for a brief moment for the hitter to collect himself after an inside pitch. I’d have the umpire is to call a strike if the hitter insists on stepping out after one warning. Keep calling strikes every five seconds or so until he does step in.

BASKETBALL... A couple things on free throws annoy me.

The double bonus. Gone if I’m in charge. Part of the original rationale was that this would speed up the game by cutting down on late game fouling. That obviously didn’t happen. And, it takes longer to miss two free throws than it does to miss one.

Airballs on free throws. I lean toward a technical foul and disqualification on the spot for an airball from the free throw line. Hit the rim, hit the backboard. At least then, there is a chance.

Traveling. Some officials do a great job of calling it by the book, others don't.

FOOTBALL...
Allow returns from the end zone in high school.  I’d also like to see returners in high school and college who touch a knee while trying to field the ball and with no one within 5 to 10 yards (a negotiable point here) be allowed to attempt a return.

Holding. I like the high school enforcement better than the NFL. 10 yards from the spot of the foul.

Halftime: The NFL has it right with 12 minutes for all their games except for the Super Bowl. And the Super Bowl telecast would be more watchable. College and some high school halftimes seem to last forever.

PAT kicks. The NFL wanted to put some uncertainty into the point after. I’d require the guy who scored to attempt the kick. We might see more two point conversion tries as a result. And that wouldn’t be a bad thing either.