Kyle Nelson is on the Comeback Trail for the Diamondbacks

The left-hand reliever is returning from surgery, and will look to beat his projections

Arizona Diamondbacks Kyle Nelson (24) pitches against the Colorado Rockies on Opening Day at Chase Field. | Joe Rondone/The Republic / USA TODAY NETWORK

Projecting relievers' performances is always risky business, especially with ones that don't have a lot of major league innings or are coming off injury.

Such is the case with left-hander Kyle Nelson. He had to undergo Thoracic Outlet Surgery in early May of 2024, and never made it back to the team last year. Thus his ZiPS and Steamer composite projection below is based on a small sample size.

Kyle Nelson, Left-hand reliever, age 28

Kyle Nelson 2025 Projection | Jack Sommers

Nelson is projected to be right around a league average reliever in terms of ERA, walk and strikeout rates. He throws the slider between 50-60%, with a low 90's four-seamer and cutter, which has been his least effective pitch.

Why Kyle Nelson might outperform his projection

Nelson's career ERA is inflated by a poor start to his career with the Cleveland Guardians. Since joining the Diamondbacks in 2022 he has a 3.47 ERA, 0.79 better than his career mark, and over a half run better than his projection.

In fact Nelson posted a 2.19 ERA in 2022, and had a 2.60 ERA up through the All-Star break in 2023, before tiring in the second half and finishing with a 4.18 mark. In 2024, Nelson did not allow a run in his first eight games, 9+ innings, giving up just three hits and walking two while striking out seven.

But the injury that sent him to the surgeon's office had started barking, and he gutted out three games in which gave up runs in each. He finally told the team about his discomfort.

Nelson is expected to be fully recovered and ready to go in spring training. He is a tough competitor, who has had to fight for a roster spot every year of his career. He will certainly continue to carry that mindset into 2025.

Why Nelson might underperform his projection

Even while healthy, Nelson's peripherals over the last three seasons have not quite supported his D-backs 3.47 ERA. During that time he's posted a 4.09 FIP (Fielding Independent Pitching) and an expected ERA from Statcast of 4.05.

These numbers would suggest the forecast is right on the mark. However it's impossible to predict what kind of stuff he'll have coming off major surgery, and especially how it might affect his slider. Such heavy slider usage is generally a red flag when it comes to pitcher health. Nelson does not have the fastball to survive without a heavily-used plus plus slider.

Summary

Kyle Nelson has had long stretches where he's been very effective for the Diamondbacks. But health and recovery from surgery are question marks and could lead to another short season.

He is projected to only pitch 32 innings as it is, and he is an unlikely candidate to reach or exceed his previous career high of 56 innings.

If Nelson makes the roster, he will slot in behind A.J. Puk and Joe Mantiply as the third short-outing lefty. Expect him to split time between MLB and Triple-A Reno, limiting his major league innings further. But don't be surprised if he puts up good numbers in that time. He's done it before.

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