Strength of Players Faced and the Impact on Player Output

So the World Series is complete and the Boston Red Sox are champions. The team with the best record over the season won the playoffs, that doesn’t happen often so the usual discussion of the value of the playoffs compared to the regular season will happen less this off-season.  We can now move onto the awards season. At the time of writing no awards have been given, so here is my slightly new method of determining how good players are. This only looks at offense for batters and a look at something slightly different than normal for pitchers.

If you look at the Fangraphs leaderboards for WAR in 2018 you will see 2 Indians players in the top 5 AL batters (Jose Ramirez & Francisco Lindor) and 4 pitchers in the top 10 AL pitchers (Trevor Bauer, Corey Kluber, Carlos Carrasco & Mike Clevinger). Now you might say that the reason they are so high is the fact that they played in a division which was one of the worst of all time and therefore the homers and strikeouts they got were easier than ones got by others.

Is that fair to think that these players got an easy ride, how would we determine if that is the case or not? To do this I have looked at batter and pitcher wOBA (weighted On-Base Average) for the season and created a statistic based on the strength of the players they have faced. I have called this SOPF (Strength of Players Faced) and it is calculated by taking the average end of season wOBA of all the players they have faced for the season, to give the average output for that player. For example if a batter had 10 PA against a pitcher with a .300 wOBA and 10 PA against a .330 wOBA pitcher, their SOPF would be .315

( ( 10 PA * .300 wOBA + 10 PA * .330 wOBA ) / 20 Total PA ).

For batters a higher SOPF means he has faced easier pitchers as they averaged a higher wOBA overall. For pitchers a lower SOPF means he has faced easier batter as they averaged a lower wOBA overall.

Below are the top 10 batters and starting pitchers who have faced the easiest opposition in 2018. (Batters have faced at least 200 PA & Pitchers have faced at least 500 PA).  The league average wOBA is 0.315.

Well there we go, 6 Indians players in the top 10 for the batters. But this isn’t as conclusive as we might of liked. Look at both those lists, does something stand out to you?  All of the batters are from the AL and all of the pitchers are from the NL. This skew is the effect of pitchers batting in the NL, they have a combined wOBA of .132 in 2018 compared to the league average of .315. To make sure this analysis is as far as possible we need to remove the pitcher batting from our calculations.  Doing that gives us the following top 10s, same criteria as before. The league average wOBA without pitchers is 0.320.

This now gives us 5 Indians batters in the top 10 and 2 Indians pitchers, so it definitely looks like they played against weaker players for the season. To put these values into more context the maximum difference from the average is 0.011, for both Roberto Perez and Francisco Liriano, which is 3.6% of the league average. These Indians players had an easier season but the overall factor was less than 3% for most of their players.

Using the newly created SOPF, I can now create a stat for how good a player is. This looks at how much better a player is than the rest of the league accounting for who they have faced. I have called this EOI (Effective Output Increase) and it is calculated by subtracting a player’s SOPF from their wOBA. So, who according to EOI are the best hitters and starter for the 2018 season.

The above table has the top 10 hitters for EOI, minimum 200 PA, as you can see from their wOBA rank these players are all up there as being the best hitters just the order is slightly changed. The two things that jump out, is one, that this metric has put Mike Trout as better than Mookie Betts due to Trout’s lower SOPF, which says he played against better pitchers than Mookie did. And two, this lower SOPF that Angels players faced also elevated Shohei Ohtani up 4 places.

Those are the best players but whose overall ranking has been changed the most. If we look at players that ended up in the top 50 for EOI, the biggest gainer is Shin-Soo Choo who jumps up 23 spots. The biggest loser is Francisco Lindor who drops 10, his fellow Indians infielder Ramirez is also high up the drop list dropping from 9^th overall to 16^th.

The table below has the top 10 starters for EOI (minimum 500 PA), as with the batters the list is mainly unchanged but has the top 2 switched around. The EOI credits more to Jacob deGrom than Chris Sale due to his higher SOPF, deGrom faced batters that were on the whole better than average where as Sale faced ones who were worse. The only major change in the top 10 is Bauer, who drops below Justin Verlander, Max Scherzer & Gerrit Cole due to his lower SOPF.

If we once again look at players that ended up in the top 50 for EOI, the biggest gainer is Jack Flaherty who jumps up 12 spots. Flaherty had the highest SOPF of any starter with 500 PA under their belt.  The biggest loser is Alex Wood, who drops 10 and as with the drop list for batters there are two Indians players there. Clevinger and Carrasco dropping 6 places each.

Like all stats in baseball this one needs to be taken in context with other factors and stats when making a decision about who the “best” or most “valuable” player is.  But this gives me more information about if players got help from playing poorer teams. If we are looking at the Indians players, yes their numbers are boosted by playing in the poor AL Central.

My next step with this stat is to see how the top players have reached their increase, did they perform well across the board or did they hit better against the weaker pitchers. And vice versa for pitchers.  Look for an upcoming piece about that.