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Why Colby Rasmus could be an elite Left Fielder for the Rays in 2017

MLB: Texas Rangers at Houston Astros Troy Taormina-USA TODAY Sports

To be honest, I’d been such a proponent of adding Jose Bautista to the Rays that the Colby Rasmus addition caught me off guard. It’s not that Rasmus seemed like a bad addition, or that the price point wasn’t right, I just didn’t understand the attraction. That was the case until I delved deeper into the defensive impact he will have in left field, where the Rays needed more depth.

To get a feel for his past performances, let’s look at how it impacted the Astros in 2016, and compare that to Rays left-fielders. Then we’ll take a peek at whether it was an anomaly, and take a look at his worst peripherals to keep our outlook grounded.

In the interest of clarity, we’ll break it down into three significant defensive statistical categories and include team performance. That should enable a decent evaluation of how significant a change Rasmus may make in left field.

ARM - The amount of runs above average an outfielder saves by preventing runners from advancing

Rasmus represented 46% of the Astro’s innings in LF and was the only player in LF to provide them with an ARM rating greater than 0.6. He was definitely their best in that category (6.7 rating), contributing enough to make the Astros tops in MLB. The Rays, meanwhile, were 16th overall.

ARM Ratings for 2016 (Team or player, MLB Ranking in bracket)

  • Astros: 7.2 (1)
  • Rasmus: 6.7 (1)
  • Rays: 0.4 (16)
  • Dickerson: 0.0 (47)

Not only was Rasmus the best player on the Astros in ARM rating, he was also the best of all of MLB left-fielders with at least 100 innings at the position. Let’s go ahead and call this one a significant upgrade for 2017.

RngR - Range; in other words, Is the player an Ozzie Smith or an Adam Dunn? Do they get to more balls than average or not?

Once again, Rasmus was the only Astros LF to provide a significant above-average range rating in 2016. Other than Rasmus, Only Jake Marisnick (0.5) was rated above 0.

However, this is one area in which the Rays, and Dickerson, look better:

RngR Ratings for 2016 (Team or player, MLB Ranking in bracket)

  • Astros: 1.7 (14)
  • Rasmus: 4.0 (7)
  • Rays: 4.9 (10)
  • Dickerson: 6.5 (3)

The fact that the Rays now boast two left-fielders that were within the best 7 in range rating in 2016 bodes well for outfield defense. We’ll call this one a draw, possibly a slight downgrade in range when Rasmus is there, but still outstanding range overall.

If Rasmus and Dickerson split time in LF, Kevin Kiermaier can rest assured that he’ll get plenty of support. As noted by our own JT Morgan in September, the Rays benefited from a tremendous LF performance from Dickerson in the 2nd half of the 2016 season thanks to his range.

UZR/150: UZR tells you how many runs better or worse that player has been relative to the average player at his position, adjusted to 150 games for comparison purposes

With an overall view of their defensive output in 2016, the UZR points to a significant improvement for the Rays in LF for 2017. Although Dickerson more than held his own and provided the Rays with a strong performance, Rasmus was one of the best in MLB, showing above-average strengths in all defensive areas.

  • Astros: 11.1 (4)
  • Rasmus: 31.8 (5)
  • Rays: 5.4 (10)
  • Dickerson: 14.5 (21)

This points to a pretty significant upgrade for the Rays and there’s no denying that he should be the primary LF option in 2017, enabling Dickerson to DH more often.


Rasmus’ 2016 performance earned him consideration for the Gold Glove award, an indication of just how strong his work in LF is. That’s something Dickerson wasn’t able to provide, despite some great work. Although Rasmus was beat out by Brett Gardner, the metrics agree with those who believe Rasmus was the best defensive left-fielder in the AL for the 2016 season.

There’s also a decent argument to be made for the Rays to consider using Rasmus in RF on occasion. With such great range and a great ARM rating, he should profile well there when needed.

But was 2016 outlier for Rasmus? A one time occurrence?

Simply put, no.

Past Performances

Although his 2016 defensive rating of 11.1 was high, it was actually the 3rd time he was rated above 11. In 2009, while with the Cardinals, he managed an 11.5 rating through 147 games, and in 2013 he managed his best season ever for the Blue Jays with a rating of 12.9 through 118 games.

Even more impressive is that he was playing mostly CF in 2009 and 2013 (finishing 5th both times in Def rankings).

Essentially, Rasmus has arguably performed well enough to provide 3 Gold Glove calibre seasons thus far in his career and can be expected to provide the Rays with well above-average defensive play for the 2017 season.

What Does it Mean for the Rays?

Rasmus may provide a small edge over Dickerson in left field, but he certainly provides a huge upgrade over all the others who played that position for the 2016 Rays.

Here’s what the other LF options produced in 2016 in each of the categories listed above (100 innings and above):

  • Desmond Jennings (FA): 256.2 Innings, ARM -1.4, RngR 1.8, UZR/150 9.7
  • Brandon Guyer (CLE): 196.1 innings, ARM 0.6, RngR -2.1, UZR/150 -23.5
  • Mikie Mahtook: 150.2 innings, ARM 0.1, RngR 0.9, UZR/150 14.7
  • Nick Franklin: 132 innings, ARM -1.2, RngR -2.3, UZR/150 -24.8

It’s safe to say that Mahtook was the only real option in LF and that with his bat not producing much at this point, his presence in the OF was going to be more for defensive and development purposes. Bringing in Rasmus relieves some of the pressure on Mahtook’s bat and allows him to get some time in as a 4th outfielder, a position he is more suited for at this point in his career.

Concerns about Rasmus

Not all defensive metrics valued Rasmus’ 2016 performance. Most notable are the BIZ (88), Plays (76), and RZR ratings (.864), which temper expectations slightly to “just” above-average when using Frangraph’s chart.

However, it’s the complete package that makes him one of the best LF defenders in MLB. The BIZ and Plays statistics place Rasmus outside the top 30 in each category, 68th in RZR’s case. But when you combine it with his Top 12 OOZ (46), ARM, RngR, and combine everything to come up with the UZR/150, you see how impressive 2016 was for him. It’s what gave him the best LF Def rating (7.8) in all of MLB and made him a Gold Glove candidate.


As a converted believer, I now see how this signing makes sense for the Rays. I’m looking forward to seeing strong outfield run prevention in 2017 and hope it helps the Rays contend more effectively.