OK. I got some good ones this time. Or maybe not. Who knows.

• Replace all of the grass on a baseball field with dirt from the basepaths and then replace the basepaths and warning track with grass. The grass might be slightly tougher to run on for the offense, but if a ball isn't caught on a fly, it'll take much more creative bounces. Plus it would look cool, like a film negative.
  
• Headsets and earpieces so that players and coaches don't need all of those ridiculous hand signals. Imagine the precision timing of a double-steal or how much more creative pickoff attempts would be if they were coordinated via voice command.
• No longer require players to play "both sides". In other words, 9 defensive players and 9 offensive players. It works for football. Wait, I've done this one before, right?