The Colorado Rockies have a huge hole in their bullpen

On Monday, the Colorado Rockies started a pivotal 10-game homestand against National League West opponents. Prior to the first game, left-handed reliever Mike Dunn told reporters that he was due to have season-ending shoulder surgery.

"“Things didn’t go well. I had a couple of setbacks. After my second outing, I had to get a cortisone injection. That didn’t hold up either so I’m shutting it down for the season,” Dunn told Rox Pile and other reporters. “It’s disappointing that I’m not going to be able to be back this year but ultimately I know I gave it everything I could to be back. It just didn’t hold up.”"

Dunn was to be Colorado’s primary late-game out-getter against left-handed batters down the stretch had he recovered. Though he has a 5.61 ERA in 93 games in purple, his career numbers against left-handed hitters is solid, with them hitting .233 against him.

With Dunn’s injuries holding him to just 17 innings, this has been a problem for the Colorado club all year. In fact, the team is the fifth-worst in baseball by wOBA in left-on-left situations, with opponents tagging a mark of .341.

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The Rockies did not do anything at the deadline to help their southpaw problem. The addition of Seunghwan Oh helped the bullpen big time … though his numbers against lefties aren’t good. And Colorado actually let a left-hander go as they waived Zac Rosscup, who held left-handed hitters to a .140 batting average against in his career.

So where do the Rockies go from here?

Jake McGee, Harrison Musgrave and Chris Rusin make up the left side currently, with Tyler Anderson and Sam Howard being possible additions down the stretch.

Except none of those players are actually a solution to the Rockies’ problems. As you can see here, left-on-left situations have been favorable to the Rockies only when starter Kyle Freeland has been in them. The Swiss army knife, Rusin, and the rookie longman, Musgrave, have been okay … but neither is a high-leverage left-on-left guy. That has been McGee, who has frankly been horrible in that role.

Anderson could be a guy who bounces to the bullpen in September and is likely the first cut from the rotation to the pen for a playoff series. His left-on-left stats, however, are also not good. Howard, meanwhile, is seeing left-handed batters hit .316 off him at Triple-A this year.

With the Dodgers, D-Backs and Rockies all within a game of each other atop the West and Colorado having six games against Los Angeles and seven against Arizona in September, the season could very well come down to a late game left-on-left situation.

Obviously displaying these numbers shows enough evidence that this situation might not be a good for the Rockies … but breaking it down further, you find something more alarming.

Cody Bellinger is 2-for-4 with a home run and two RBI off McGee, and he’s 3-for-10 with a home run and two RBI off Anderson. However, Rusin and Musgrave are a combined perfect 8-for-8 in getting him out. Max Muncy is 2-for-5 against the current crop of Rockies relieving lefties, and Jon Jay has taken them to the woodshed getting hits in seven of his 18 at-bats against Rusin and McGee.

Even Daniel Descalso has gotten his off Rusin. Joc Pederson, meanwhile, has been taken to the woodshed by that duo of Rusin and McGee.

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The whole point of this is that you’re likely to see one of these matchups this month in a tied or close ballgame. The Rockies will turn to the lefty in their pen to get one of those batters because that’s what the game dictates. But neither the numbers nor history will be in the favor of the left arm of the Rockies’ relievers.

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