The impact of averages

by BaseballHQ.com on May 12, 2010 @ 00:00:00 PDT

 


Home runs, RBIs and stolen bases are easy categories to monitor the impact of player changes. Add a speedster to your team and you can count the stolen bases on your bottom line. But try to make an impact on a ratio category and the results are not so obvious.

And much, much less than you think.

Let's set up a scenario and monitor the results. Our assumptions... a team with 6000 full-season at bats and a .265 average. Let's isolate 540 of those at bats - one batter.

If that player is a .250 hitter, he contributes 135 hits to your team's bottom line. Replace that player with a .300 hitter and you are replacing 135 hits with 162 hits. Add those 27 extra hits to your team total and watch that batting average soar, right?

Wrong. Your .265 average becomes... .270. A nice boost, but not record-breaking. And this is if you replaced your .250 hitter with a .300 hitter at the beginning of the season.

Most of us make our trades in response to perceived weaknesses during the season. Let's replace that .250 hitter with a .300 hitter on May 1. This move would boost your .265 team average to .269 by season's end.

Making this move on June 1 would lift your .265 team average to .268 by October.

July 1? .267. August 1? .267! September 1? .266. Hardly worth the bother unless it's a close race and you have reason to believe your competitor's average will drop.

Pitcher ERAs show a bit more movement since the base of total team innings pitched is substantially lower than the accumulated total at bats. Let's replay the scenario.

Our assumptions... a team with 1200 full-season innings pitched and a 3.00 ERA. Let's isolate 175 of those IP - one starting pitcher.

If that pitcher has a 3.50 ERA, he contributes 68 earned runs to your team's bottom line. Replace that hurler with a 2.52 ERA and you are replacing 68 earned runs with 49. Subtract those 19 extra runs from your team total and your team ERA drops from 3.00 to 2.86. A noticeable drop.

But, make this player move during the season and the impact lessens. On May 1, this move would decrease your 3.00 team ERA to 2.88. On June 1, your ERA would drop to 2.90. On July 1, the impact is down to .07 to 2.93. On August 1, 2.95 and on September 1, 2.98.

Lessons that can be learned...

  1. One player will not make a substantial impact on a ratio category unless it is early in the season and the race is close. Naturally, the wider the variance in average between the two players the more of an impact you will make.
  2. You can make more of an impact on ERA than in batting average.
  3. Since pitchers are more difficult to project, the impact on their ratio categories may be greater but the probability of a successful forecast much lower.
  4. The underlying assumption is that you can project what a player will do over the balance of the season. Replacing a .240 BA player with a .350 BA player is fruitless if both players bat .270 the rest of the year.
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