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Cole Hamels' consistent April struggles

A look at Cole Hamels in 2015 without using words like “trade,” “surplus value,” or “Blake Swihart.” Why does the southpaw struggle in April? PITCHf/x data might be able to help us figure it out.

Cole Hamels struggles every April - can Pitch F/X help explain why?
Cole Hamels struggles every April - can Pitch F/X help explain why?
Bill Streicher-USA TODAY Sports

Philadelphia Phillies' ace Cole Hamels has been on the receiving end of some of the hottest takes baseball has to offer, both during the off-season and amid his early season struggles. Articles about his Major League-leading home run total and high number of walks have been written, with the worry being that he's in for a rough season. However, there has been a curious trend throughout his career that is at least worth a passing examination. Hamels has been, relatively speaking, bad in the month of April. Historically, this month has been the southpaw's worst in terms of ERA, FIP, AVG, OBP, SLG, wOBA, Strike %, HR/FB Rate, and BB %. Observe:

Month IP ERA AVG OBP SLG wOBA Strike % HR/FB K% BB% BABIP FIP xFIP
Apr 255 4.02 0.244 0.310 0.421 0.319 65.1% 13.00% 23.60% 7.80% 0.296 3.90 3.51
May 312.2 3.63 0.238 0.294 0.414 0.308 66.4% 12.60% 24.30% 6.30% 0.291 3.59 3.27
Jun 318.2 3.33 0.235 0.291 0.402 0.299 66.2% 12.10% 22.30% 6.60% 0.277 3.80 3.54
Jul 313.2 3.16 0.224 0.280 0.379 0.289 67.1% 10.70% 22.90% 6.10% 0.268 3.59 3.51
Aug 313 2.70 0.237 0.276 0.364 0.279 68.4% 8.70% 21.70% 4.30% 0.285 3.13 3.32
Sept/Oct 312.1 2.97 0.228 0.286 0.359 0.285 65.5% 10.50% 24.90% 6.50% 0.286 3.19 3.16

Approaching this with skepticism is warranted, as this is combining what appear to be unrelated performances 11 months apart. However, every April is preceded by a four month break and Spring Training, so that's a factor that potentially means something. That said, no conclusions will be drawn here about why this trend occurs. This article is primarily interested in examining if this ineffectiveness is random, or if there is a demonstrable difference in the quality of Cole Hamels' pitches at the beginning of the season.

One point of interest in the above data is that while his HR/FB rate is high and BB% far worse than in all other months, Hamels is still striking out batters at a typical rate. There is also a noticeable difference in his Strike %, with his 65.1% clip in April being below his career 66.7% rate in the remaining months.

Hamels throws a four-seam fastball, one of the league's best change-ups, a cutter, and a curveball. Looking at Pitch F/X data (2008-2015), each pitch can be examined  for its average attributes during April, and then in the rest of the season.

Time Period Pitch Count Velo MoveVert MoveHoriz SpinRate SpinDir GB% LD% FB% PU%
April FF 1545 90.90 11.36 4.34 2410 159.00 40.6% 20.6% 27.4% 11.3%
Rest of Season FF 9916 91.34 10.89 4.68 2398 156.69 40.6% 21.1% 28.4% 9.8%
April CH 987 81.91 7.28 7.79 1936 133.81 51.6% 19.9% 22.4% 6.2%
Rest of Season CH 5386 82.43 6.95 7.77 1926 131.95 56.1% 17.6% 19.6% 6.7%
April FC 654 88.11 9.34 -1.06 1830 186.52 53.3% 13.3% 23.3% 10.0%
Rest of Season FC 2186 88.83 8.11 -0.44 1637 183.26 50.2% 20.0% 24.4% 5.3%
April CU 299 74.92 -5.13 -2.84 1044 273.64 45.0% 32.5% 17.5% 5.0%
Rest of Season CU 1925 76.23 -3.96 -1.57 791 248.91 50.2% 19.7% 24.3% 5.9%

Looking at this table, what becomes immediately obvious is an unsurprising point - Cole Hamels gains velocity throughout the year. Most pitchers see some kind of a small bump, and early season run scoring isn't significantly higher than any other time of the year. It isn't likely to be the single key factor.

What is a little more interesting is that all four of his pitches exhibit a higher magnitude of vertical movement. His four-seam, change-up, and cutter are breaking less than his rest of season average, and his curveball is breaking, on average, 1.27 inches more than in other months. His cutter and curveball each see a significantly higher spin rate (in RPM) than in later in the year as well. Typically, more movement is thought of as better and less vertical drop might have something to do with his early season woes, although this isn't definitive at all.

If his pitches are moving less, it might give batters a better opportunity to judge where the pitch will finish, leading them to take pitches and be more selective and there's some evidence hitters are being more selective against Hamels early in the year.

Time Zone Swings/Pitch Whiffs/Swing Whiffs/Pitch
April In Zone 64% 17% 11%
ROS In Zone 67% 19% 13%
April Out Zone 35% 37% 13%
ROS Out Zone 37% 36% 13%

While not proving it, the results here are fairly in-line with that hypothesis. Cole Hamels throws fewer strikes in April, and batters swing less frequently.

Batters tend to draw more walks, and as they are also swinging less frequently at pitches in the zone, Hamels still earns a fair number of strikeouts. If a batter does swing at a pitch in the zone, they are less likely to miss, and with pitches in April seeing less vertical movement, it's typically swinging at a pitch left high over the plate, resulting in more home runs.

It's not a conclusive explanation by any means, and it doesn't explain why Cole Hamels is worse. It does potentially explain how he's worse, and that there's potential to feel optimistic about the rest of his season, assuming he follows the same pattern of annual improvement. Something about Hamels leads him to hang a few more pitches in April, but he seems to work his way out of it every year.

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All data courtesy of FangraphsBrooks Baseball, and Baseball Savant.

Spencer Bingol is a contributor at Beyond The Box Score. You can find him on Twitter @SpencerBingol.