Can the Sheriff Help Restore Order to the Bullpen?

The Diamondbacks have brought back left-handed reliever Andrew Chafin on a one-year deal. Chafin is set to make a $5.5 million salary for the 2023 season, which likely suggests an important role in the backend of the bullpen. That likely means he'll be asked to pitch in high leverage situations, facing some of the toughest left-handed hitters as well as right-handed bats off the bench without a safety net.

In 2022, Arizona left-handed relievers struggled to get outs in this situation. This is how Joe Mantiply and Kyle Nelson performed in this split according to Fangraphs.

Player	BF	Opp BA	wOBA Allowed
Joe Mantiply	79	.414	.466
Kyle Nelson	24	.211	.322

The lack of a reliable left-handed relief option who can handle those situations was one of many issues that affected the bullpen last season. The good news is Chafin has performed well in high leverage situations in the last two seasons, with opposing hitters mustering just a .237 wOBA in 2022 and .270 in 2022. The D-backs are banking on a repeat performance in 2023, which is a big risk as the lefty will turn 33 in June. If he can repeat that performance however it would allow the rest of the bullpen to settle into more fitting roles.

The biggest reason for Chafin's improvement in that situation the past two years has been improved command. Free passes have been an issue in past seasons with Arizona, but he's managed back-to-back seasons with a walk rate better than the MLB average of 8.4%. 2022 also saw an increase in strikeout rate to 27.6%. That strikeout rate is 2.5% higher than any D-backs reliever that threw at least 10 innings in 2022.

What made Chafin effective in 2022 started with his ability to jump ahead in counts. He threw a first-pitch strike against 63.4% of batters he faced, a career high. By jumping ahead in the count, that allowed him to lead hitters out of the strike zone. Chafin ranked in the 89th percentile in chase rate. His preferred put-away pitch was his slider, in which batters hit .085 and managed just a .129 wOBA. Over 60% of the swings against the pitch came up empty.

Location also played a role in his 2022 improvement, as his pitch heatmaps for the 2022 season were exactly where you want those pitches to end up. Not only was he able to throw strikes, but throw strikes in locations where hitters wouldn't make loud contact.

The biggest risk for the D-backs is Chafin's age, as he'll be entering his Age 33 season. He's already lost two MPH from his peak velocity of 93.8 MPH in 2019, but has been able to manage it with the ability to throw quality strikes. Any more decline in fastball velocity and movement could spell disastrous results for both Chafin and the D-backs bullpen. The key will be for him to continue to spot the fastball on the corners to jump ahead of hitters and use his slider as a put-away pitch.

Overall, I would expect Chafin to be a key member of the 2023 bullpen due to his important role. An improved bullpen is critical for the D-backs to build on a solid second half finish in 2022 and push themselves into a possible contender for the Wild Card race.