MLB trade deadline: Dan Jennings provides long-term relief for Rays bullpen woes

This morning, the Rays landed the reliable veteran southpaw they've been looking for in exchange for first baseman prospect Casey Gillaspie, the Rays first round draft pick in 2013.

Dan Jennings, 30, has been good in this the sixth year of his major league career, working mostly in high-leverage situations in the 7th and 8th innings. The left-hander currently has a 3.45 ERA, over 44.1 innings, with a 20.5% strikeout rate and a 10.3% walk rate. The ERA is over his career mark of 2.86, but the peripherals are right in line. This season has been marred by a high HR/FB rate of 24%, but he doesn’t have a history of being homer prone, and intriguingly, five of the six homers he’s given up have been against right-handed hitters. More on that later.

Jennings is more than a rental, as he's under team control for two more years—an added bonus that must have appealed the Rays' front office.

Jennings’ season ERA of 3.45 might not sound impressive the same way those of RHP Pat Neshek or LHP Justin Wilson do, but Jennings has been just as impressive of late, sporting a 2.25 ERA, .146 BAA, and 26 strikeouts in 24 innings of work since June 6. That’s just six earned runs in his last 23 appearances, holding opposing batters to an underwhelming .491 OPS against him during that stretch.

Jennings has been extremely durable in 2017, tied for second in the American League with 48 appearances this season. Most importantly, as Adam noted earlier today, he's been dominant against left-handed batters.

Thus far in 2017, Jennings has been dominant against left-handed batters, holding them to a slash of .164/.286/.211. Control at times has been problematic for him, walking opposing hitters around 10% of the time over his career, but nonetheless, he’ll certainly be an effective weapon for Kevin Cash to look to late in ballgames.

Harder on Lefties—A Change In Approach

Dan Jennings wasn’t always a pitcher who excelled at getting left-handed hitters out. His career split is actually pretty neutral, and towards the start of his career he sported reverse splits. Relievers and splits can be tricky to work with, since they work in small sample sizes, but for Jennings there has been a change in approach that corresponds with the change in results.

Through his rookie season, as compared to the present, Jennings increased his reliance on his slider, while dropping his four-seam fastball usage significantly and instead throwing a two-seam fastball or sinker.

Take a look at how Jennings pitch movement has altered over the past few years. Below is a graph of his pitch movement in 2014.

Now fast forward to 2017:

Jennings' fastballs/sinkers come lower now, and the slider movement has become more horizontal. These types of pitches typically produce ground balls and get out same-handed hitters, and it’s worked out that way for Jennings: he’s inducing a 58.5 GB%—the 14th highest rate among all relievers in major league baseball—with a significant handedness split.

The White Sox called on Jennings to be a multiple-inning reliever, mopping up for a disastrous rotation on the South Side. With the Rays, it’s comforting to know he’s capable of going multiple innings, but the team should be able to deploy him more effectively, picking battles against lefties and groundball-susceptible batters.

For a team in desperate need of quality arms in the bullpen—specifically a reliable southpaw—the acquisition of Dan Jennings seems like a good under-the-radar pickup for a team in the thick of a playoff race.

He is expected to join the Rays tonight for the start of a four-game series at Yankee Stadium, a place where ground balls are certainly welcomed.