Colorado Rockies: Jake McGee’s effectiveness very much tied to velocity

DENVER – Jake McGee has been one of the best relievers in baseball at points in his career. But, in two of his three years with the Colorado Rockies, the left-hander has been not that.

In 2018, the 32-year-old McGee has two key marks that are the worsts of his career. Both his 6.35 ERA and 1.44 WHIP for the Colorado Rockies are low-marks for the lefty.

Underlying those marks is his fastball, which is also bottoming out at a career-low of an average velocity of 93.5 mph.

So are those two things connected besides just a basic coincidence? Very much so.

Rockies manager Bud Black may have said it best after McGee had a one-and-two-thirds innings scoreless appearance on Friday against the Dodgers.

"“We’ve talked about who is Jake McGee,” Black said. “And my expectation, my visual is Jake turning it loose with velocity and letting it rip going after guys. That’s more like it, and that’s what I said to Jake after the game, ‘That’s what we need to see from you’ and he delivered.”"

You can actually see the sharp drop off in McGee’s velocity the past few seasons below and also overlay his stats: 4.73 ERA with an average fastball of 94.2 mph in 2016 and 3.61 ERA with an average fastball of 94.9 mph and see the trend continues.

Now you might be saying, there was only a seven-tenth of a mile per hour difference with his average fastball velocity from 2016 to 2017. Does that really matter?

Yes.

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Across the Statcast era, when throwing his fastball 95 mph or more, batters hit .230 off of McGee. When throwing 94 mph or below, batters hit .276. OK, that’s a difference. However, there’s actually a better number for this … and it needs a sabermetric explanation.

The stat we’ll use is xwOBA (expected weighted On Base Average), which is a lot less complicated than it sounds. Similar to OPS, it’s a stat that realizes on base percentage is important, but that not all hits are created equal. That’s the OBA part — simple — rate stat that helps equate a batter’s total value. The w part is weighted, which just means that it equates for things like pitching at Coors Field, hitting at Petco Park or being in the American League. The x part is expected and it’s a new thing Statcast is using that calculates what wOBA should be based on launch angles, exit velocities and history.

So let’s talk about McGee’s fastball. When throwing it 95 mph or above, his xwOBA against is .280. When throwing it 94 mph or less, it’s .395. According to Fangraphs, that’s the difference between “awful” and “excellent” for a hitter.

Put bluntly, McGee’s success is almost exclusively based on his ability to throw hard.

Here’s the bad and good news for the Rockies.

McGee has never thrown slower than he has this year … but his velocity has been increasing almost all season. Lately, he’s seemingly gotten back to being the fireballer that other teams fear and the numbers back this.

While a very small sample, McGee has only allowed one earned run in his past four innings pitched.

Based on McGee’s velocity over the past three outings, he could be returning to form. If you think that it’s a stretch to say that, I’ll put it this way. With the way the Rockies bullpen has been going this year, even three games in a row of moderate success is worth writing about glowingly.