Ian Desmond has always been a contact hitter with an aggressive approach at the plate with a low walk rate and a relatively high strikeout rate. This means that his value is dependent on his ability to get hits and on his power. The decline in those numbers are worrying.
2013 2014 2015 Batting Avg .280 .255 .225 On Base % .331 .313 .277 Slugging % .453 .430 .341
The drop in batting average is certainly far from good, but the massive drop in slugging percentage is really painful to see. His ability to pump out 20 to 25 home runs per year has been a calling card, and now at age 29 he is suddenly on course for a 9 HR season.
I am mostly interested in Desmond's power today, but let's look at his plate discipline numbers for a moment.
His walk rate this year is normal. His strikeout rate is high, but generally in line with the past two years. While more of his strikeouts are of the looking variety, this side of things is not going to explain his problems.
Desmond is swinging at more pitches than he did the past two years and he is also making more contact than ever. He is indeed chasing pitches out of the zone a bit more frequently and missing too often, but the difference from years past is too small to explain this decline by itself. (Numbers from Fangraphs)
So what happens when Desmond does put the ball in play?
2015 Career Line Drive % 14.9% 18.0% Ground Ball % 58.5% 49.6% Fly Ball % 26.6% 32.4%
Since we are looking at power, these numbers have especially large implications. Home runs come from fly balls, and a guy who wants to hit 20+ HR in a year can't afford to be hitting a ton of ground balls. To help you visualize the impact of this, here are some numbers that represent total bases divided by at bats (TB/AB) for each type of contact by several players with different amounts of power (career numbers):
Span Desmond Harper Grounders 0.29 0.29 0.23 Fly Balls 0.42 0.75 0.97 Liners 0.89 1.01 0.98
As you can see, as power increases not only do line drives become more valuable but fly balls become very important as well. Each of Desmond's line drives is worth three grounders, and each fly ball is worth two and a half grounders. A Harper fly ball is worth more than two Span fly balls, which reflects that kid's extreme power. Desi has medium power, and it is worth exploiting.
It appears that Desmond's power numbers are low simply due to an issue of deceased altitude. He is not driving the ball into the air enough and it is driving down his numbers dramatically. He in on pace for 9 HR and 46 doubles, which is not terrible but not what we expect to see from him.
Fewer home runs and more doubles suggests the possibility that Desmond isn't hitting the ball as hard as he used to, and yes, overall he is not hitting the ball as hard if you count all the ground balls he is hitting. When Desmond hits a line drive or a fly ball, he is averaging the same distance he has in years past, which indicates that his physical ability to drive the ball when he makes good contact has not gone anywhere. Here's all his line drives, fly balls and home runs in recent years:
# in play Distance Angle 2015 28 263 0.23 2014 171 268 6.08 2013 192 262 4.19
The distance numbers are very consistent. We already knew that the pace at which he is hitting balls to the outfield has decreased (he's on track for ~130 # in play for the season). Unfortunately, I am not enough of an expert to explain the hidden meaning of angles, but there does appear to be a correlation between high angles and HRs. (numbers from Baseball Heat Maps)
Clearly, Desmond's power has not gone anywhere yet, but he is not producing because he has stopped using his power efficiently. I can only speculate as to whether he is having pitch selection issues or whether his mechanics of his swing are off or if it is just rotten luck, but something is not right there. One other abnormality is the fact that he is driving the ball to the opposite field as much as in years past, but again I can't say whether that is due to a mechanical change or a change in the timing of his swing. The numbers can only tell me so much.
Desi's power is not gone forever. He's just hiding it really well.
The takeaway is that Ian Desmond will return to hitting home runs as soon as he starts hitting the ball into the air more. He hasn't forgotten how to make contact, but for whatever reason he is driving the ball into the ground at a much higher rate than in the past. It is probably a mental thing or a swing thing and has nothing to do with his age. He may continue to slump, but hopefully Desi and his coaches are working hard to identify what has changed at the plate from past seasons, whether mechanically or mentally. Power is worthless if it is not used.
Thanks to his power, Desmond will find success if he can consistently put the ball into the air even if he never figures out how to increase his batting average. If he can do both, he'll be producing at an above average rate again in no time. Here's hoping that he's back to his normal self soon.