Trying to compare Mariano Rivera to other pitchers is like trying to compare a photon to other sprinters. Out for out, the difference between him and Pedro Martinez is the difference between Pedro and a league-average player. He hasn't had a full season much better or worse than any other, but he's been an order of magnitude better in October than he's been in any other month. Nothing about his career makes any sense.
Rather than ask how much better Rivera has been than anyone else, let's look at how weird baseball would be if everyone else were as good as Rivera. What if we cloned him, had him pitch every inning of every game, and assumed he'd be just as effective? Call it Mo League Baseball.
Half-off scoring: If every pitcher were Mariano Rivera, the hitters would turn into pitchers: In his relief appearances, opponents have hit .205/.256/.280 off him, which is in line with decent-hitting pitchers like Bob Gibson or Livan Hernandez. Out of the bullpen, Rivera has created an environment in which teams score around 2.22 runs per game (earned and unearned). That's lower than the average of the worst offense in the worst year for offense in major-league history (1908 Cardinals, 2.4 runs). And it's about 2 runs per game less than teams are scoring this year, and less than half of what they scored in 2000.
What's left of the offense gets weird: In the modern game, there isn't a big difference between designing an offense to score as many runs as possible and designing one to score more runs than the other team. With Rivera pitching both for and against them, managers would play to score one more run than the opponent because any lead would probably be permanent. The value of a particular hit, steal, or sacrifice would depend heavily on the situation, so contextual stats like Win Probability Added would become more valuable than Wins Above Replacement.
New strategies and roles: Mo League Baseball would be like the dead-ball era but with home runs and strikeouts. Teams with smaller parks might try to fill their teams with sluggers, while others would forgo the homer altogether and win with Baltimore chops and speed. Managers would occasionally put their best hitter on the bench to start the game. The highest-paid positions would be pinch-runner and catcher.
New defensive positions: With weak contact and more small-ball, the defense would be fluid over the course of a game. Some situations and batters would call for five infielders, and some managers might adopt a rover-type position permanently to stop BULLSHIT LIKE THIS. Look at the shifts Tampa Bay is already using. Joe Maddon wants Mo League Baseball to happen.
Shorter games: There would be more pickoff attempts, but with no offense and all commercial breaks replaced by a two-second still of Rivera smiling, games would routinely finish at 90 minutes.
Ninety minutes! Case closed. After Mo learns how to do knee surgery, performs it on Iman Shumpert for practice, does it on himself, and picks up the knuckleball, we need to go right to the factory he came from and make a bulk order.
Image by Jim Cooke