I am not a fan of sports. To be honest I find them to be boring. However, there are a few things that could be done to make any sport more entertaining to watch.
First thing every sport needs is mandatory steroid injections. Bigger player, with more aggression, the kind of aggression that wold lead to much violence and injuries on the field. In rare cases players of any game might get worked up enough to kill one another. Imagine placing a bet on which player will lose control next, and take out a few members of the team. This could help any sport, and would equal a much high entertainment value overall.
Now some things would help one sport but not another. Baseball is by far the least entertaining sport to watch. The solution to this problem is easy, one in every 50 balls will actually be a high explosive set-off by impact. Just think, the windup, and the pitch, and then BOOM. Sure the players would be risking death, but they would finally have a reason for their much inflated salaries.
Soccer is a sport no one in the US cares about, and mostly enjoyed by the other parts of this world. The field is what need changed. The game would now be played on a platform, the platform would be the same as a soccer field is now, however under the platform the is a pit of fire and spikes. So at random times and locations during the game the upper platform opens trap doors and if we are lucky some one falls in. Now that would make US give a shit about soccer.
A few other thoughts. Football, release rabid animals on the field every few plays. MMA, give them knives.