Answer: Crime increases
In this case, we are talking about major league pitchers deliberately throwing at batters, called "Hit By Pitcher" or HBP. In 1994, the HBP rate exploded. Why?
Before 1994, if a pitcher deliberately hit a batter, the batter's team would retaliate.
After 1994, the rules changed to a "warning-then-eject" rule. Once the “warning-then-eject” rule was implemented, teams effectively got a free HBP, with no fear of retaliation. Team A hits team B, then both teams get warned and team B can’t retaliate without automatically losing their pitcher and manager! They de-incentivized retaliations to such a degree that they actually incentivized the first HBP.
HT: Eric E.