Sweeper Specialist Ethan Roberts is a Breath of Fresh Air in Cubs Bullpen

The second-half success of the Chicago Cubs bullpen has been much discussed--as it should be. Their 2.55 second-half bullpen ERA leads baseball. Their 1.9 Fangraphs WAR is fourth. Jorge López and Tyson Miller have been fantastic additions, and Porter Hodge looks like a good, dependable, homegrown arm. 

There’s been one other, less heralded hurler who has helped the team fortify their relief corps, too: Ethan Roberts. Roberts had been something of an afterthought, after making the Opening Day roster two seasons ago and succumbing to Tommy John surgery just 7 ⅔ innings into his major-league career. After taking 2023 off to rehab, he’s back in 2024, contributing 12 innings to the major-league bullpen to this point. While 12 innings aren't much to go on, the bespectacled righthander has allowed just one earned run in those frames--the glasses, and also the innings. 

But frankly, I am not even here to talk about Roberts’s success, and whether or not it will continue. I am simply here to talk about how fun he is to watch. At 5’10” and 180 pounds, he doesn’t look like a typical major-league pitcher. This already endears me to him. I’ve always found satisfaction in athletes who succeed despite what many would consider an undersized frame.

Of course, if someone is that small, they probably aren’t throwing especially hard. Roberts doesn’t, which I also take satisfaction in, in the era of so many high-velocity fastballs. Among 652 pitchers who have thrown at least 100 pitches this season, Roberts’s average pitch velocity of 84.3 mph is 630th, according to Baseball Savant. A flamethrower, he is not.

Apart from a four-seam fastball that he has thrown just nine times all season, Roberts is primarily a two-pitch pitcher. Per Baseball Savant, he features a cutter that he throws 34.7 percent of the time, and a sweeper that he throws 61 percent of the time. Throwing a sweeper that often is already an anomaly. As a matter of fact, only one pitcher, Bailey Horn, has thrown a sweeper more often this season.

Not only does Roberts throw his sweeper often, he also gets a ton of movement on the pitch. It drops 3.6” more than the average sweeper at a similar velocity. That’s 18th of 110 pitchers who have thrown at least 100 sweepers. Where this sweeper really shines, though, is in the horizontal movement. Roberts’ sweeper has 4.9 more inches of break than the average sweeper at a similar velocity. This leads all of baseball. In fact, the next-closest pitcher, Greg Weissert, is at 4.4”.

To better visualize this, here is a chart of all 110 of those sweepers from Baseball Savant. The horizontal movement relative to the average is on the x-axis, and the vertical movements is on the y-axis. Roberts’s sweeper is the dot that I circled on the far right:

Let’s combine everything. Roberts throws his sweeper more than almost every other pitcher in baseball. It has more horizontal movement, adjusting for certain factors, than any other sweeper in baseball. In what’s been a mostly joyless Cubs season, I have taken some joy in seeing Roberts spin his sweeper up there and watching hitters try to hit it. Here’s Addison Barger coming up completely empty on a beautifully located back-foot sweeper:

Here he is getting a sword out of Brandon Crawford on another beautifully located two-strike sweeper:

To be clear, all of this alone doesn’t make Roberts a successful major-league pitcher. His wOBA allowed and his whiff rate on the sweeper are only slightly above-average. But when executed, it works, and it is just an absolute joy to watch happen.

Despite his size, and despite his lack of velocity, Ethan Roberts is here and succeeding in the major leagues. I’m not sure if it will continue. He has some favorable peripherals, and some unfavorable ones. Whether he sticks around or not, I have thoroughly enjoyed watching him come in and spin wiffle balls up there. Seeing guys pump 100-mph fastballs is a lot of fun. Watching Ethan Roberts pitch is just as much so.