There have been many, many sabermetric studies on the idea of "lineup protection." Do a Google search and you can find them easily enough. The studies all come to the same general conclusion: It doesn't really exist. Players don't change their performance based on who is hitting behind them.
But fans still believe in it. Media members still believe in it. Even some people who work in baseball believe in it. When Prince Fielder was traded to the Rangers, I read and heard people talking about how Miguel Cabrera will now suffer as a result -- without the fear of facing Fielder next, pitchers won't have to throw strikes to Cabrera. It's a topic you'll never change opinions on.
After all, didn't Cabrera just win back-to-back MVP Awards? Of course lineup protection exists! Don't be silly.
Here are Cabrera's last four seasons. Can you tell which two were the ones with Fielder hitting behind him and the two that weren't?
.344/.448/.586, 108 BB
.348/.442/.636, 90 BB
.328/.420/.622, 89 BB
.330/.393/.606, 66 BB
The two Fielder seasons are the second one (2013) and the fourth one (2012). In terms of wOBA, you'd rank them 2013, 2011, 2010, 2012. Cabrera's worst season was actually the best of Fielder's two seasons, and in theory the season when Cabrera received the most "protection."
OK, but let's dig into the numbers a little deeper. One way possible way to measure whether pitchers are pitching around Cabrera or challenging him more often is to look at the percentage of fastballs thrown him. If pitchers don't want to walk him -- and thus face Fielder with a runner or runners on base -- than Cabrera should see more fastballs to hit since the fastball is the easiest pitch command.
Here are the percentages of fastballs thrown to Cabrera the past four seasons:
2010: 52.3 percent
2011: 53.8 percent
2012: 54.0 percent
2013: 54.5 percent
OK, he has seen a few more fastballs. What does that mean in terms of total pitches? Cabrera has averaged about 2500 total pitches per season over the past four years; the difference between 52.3 percent and 54.5 percent is 55 pitches -- or about one extra fastball every three games.
What about the percentage of total pitches in the strike zone?
2010: 42.2 percent
2011: 41.5 percent
2012: 44.7 percent
2013: 44.8 percent
Again, a minor uptick -- an 82-pitch difference between 41.5 percent and 44.8 percent, or about one extra pitch in the strike zone every other game. That doesn't seem significant, especially once you factor in intentional walks (more on that in a second).
Now, there are two numbers which point in favor of Fielder helping Cabrera. He hit 68 home runs in 2010-11 but 88 in 2012-2013. That's 20 more home runs that maybe resulted from some juicier pitches Cabrera saw, right? Maybe. At the same, however, his doubles have gone down, from 93 in 2010-2011 to 66 in 2012-2013, leaving his isolated power relatively unchanged, other than a dip in 2011 when he hit just 30 home runs: .294, .241, .277, .288.
Yes, he had the injury at the end of 2013 that dragged down his final numbers; however, keep in mind that Fielder was much worse in 2013 than in 2012, and thus pitchers didn't have to "fear" him as much as in 2012. And it's true that Cabrera's walk rate increased in 2013 from the season before, perhaps because he was pitched around more (although note that the percentage of fastballs and pitches in the strike zone were basically identical both seasons).
Of interest as well is where those home runs were hit. The biggest increase the past two years came on home runs classified as being hit to "center" -- 22 versus eight over 2010-2011. Much of that is simply because Cabrera has done more damage on cripple pitches -- he hit .542 on pitches located in the middle of the strike zone the past two season versus .448 in 2010-2011, with the additional home run power.
The other category to note is intentional walks. Cabrera's intentional walks since 2010: 32, 22, 17, 19. So the intentional walks dropped a bit, particularly from 2010, when Brennan Boesch most often hit behind Cabrera.
This is the one argument you can make where protection comes into play. In 2010-2011, Cabrera batted 121 times with a runner on second and was intentionally walked 26 times (21 percent); in 2012-2013, he batted 145 times with a runner on second and was intentionally walked 18 times (12 percent). With runners on second and third, the ratios were 10 out of 29 and 5 out of 24.
So, yes, there were arguably about 10 plate appearances a season where Cabrera got to hit thanks to Fielder's protection. But also note that with Victor Martinez hitting behind him in 2011, the intentional walks were down from when Boesch hit behind him.
As for those who say Cabrera will just get a ton of free passes in 2014, here are his unintentional walk rates the past four seasons (removing all intentional walks from both total plate appearances and total walks):
2010: 9.3 percent
2011: 10.0 percent
2012: 7.2 percent
2013: 11.2 percent
He walked more often this year than the year Brennan Boesch was hitting behind him.
When you add it all up, there just isn't evidence that Prince Fielder made Miguel Cabrera a better hitter. Cabrera will be great again in 2014 because he's a great hitter.