PITTSBURGH — The Pittsburgh Pirates have had some serious issues with their bullpen this season and made a tough roster decision on one of their relievers.The Pirates are optioning right-handed relief pitcher Isaac Mattson to Triple-A Indianapolis, while recalling rooke right-handed pitcher Wilber Dotel ahead of their upcoming contest vs. the St. Louis Cardinals at Busch Stadium on May 20, according to Pirates insider Alex Stumpf.Mattson pitched 21 games in relief for the Pirates this season, with a 4.12 ERA over 19.2 innings pitched, with 15 strikeouts to 10 walks, a .253 batting average allowed (BAA) and a 1.47 WHIP.It's not a decision many would've seen coming, but it might just help Mattson get back on track and return to the Pirates even better than he was. Why The Pirates Sent Isaac Mattson DownMattson had spent all of the season with the Pirates, but he's struggled in his last five outings, with seven earned runs allowed over 3.2 innings that brought his season ERA up to 4.12.This includes a poor outing vs. the St. Louis Cardinals at PNC Park on April 30, where he came in the eighth inning with the Pirates trailing 5-4 and gave up three hits, two walks and five earned runs in the eventual 10-5 loss.Mattson also gave up three doubles and two earned runs in the bottom of the sixth innings vs. the San Francsico Giants at Oracle Park on May 10, which allowed the home to tie the game up at 4-4, blowing a 4-2 lead.He also hit a batter and gave up a double that ended up scoring a run in the 6-0 defeat to the Philadelphia Phillies at PNC Park on May 17, after coming in relief for Paul Skenes. Mattson had pitched in just four of the past 17 games for the Pirates and Dotel provides a different bulk role that the Pirates will hope he can thrive in. How Isaac Mattson Can Rejoin the PiratesThe advanced metrics aren't kind to Mattson, who has struggled with hard contact and would likely have even worse numbers base on what's expected with his pitchingIsaac Mattson Advanced Metrics in 2026StatTotalRanking (MLB)Exit Velocity91.5 mph 30th (Bottom 8%)Hard Hit49.2% 21st (Bottom 5%)Expected Batting Average.30216th (Bottom 4%) Expected Slugging %.49738th (Bottom 10%)Expected Weighted On-Base Average (xwOBA).38328th (Bottom 7%) Expected ERA6.2128th (Bottom 7%) Mattson had been with the Pirates from June 7, 2025 to now, almost a year's time spent on the major league roster. His 2025 season was exceptional, with a 2.45 ERA over 47.2 innings pitched and finally found some footing in MLB after a long journey in the minors and elsewhere.Sep 2, 2025; Pittsburgh, Pennsylvania, USA; Pittsburgh Pirates relief pitcher Isaac Mattson (72) reacts after securing the final out of the seventh inning against the Los Angeles Dodgers at PNC Park. Mandatory Credit: Charles LeClaire-Imagn Images | Charles LeClaire-Imagn ImagesThe advanced metrics from that season are way down on expected averages compared to this season, putting him more in the middle of the pack or even towards the better end. His expected ERA is at 6.21, when it was at 3.28 last season, almost three earned runs higher, a massive difference. Mattson had a great start to 2026, with a 1.13 ERA through his first 16 appearances and throwing 15 consecutive scoreless outings over a month that made him one of the most reliable arms out of the bullpen.One of the good things for Mattson is that his fastball is still averaging the same velocity, 93.8 mph, as it was last season, but he'll need to make sure he can make it more effective than he has done this season.The Pirates will likely bring Mattson back up at some point, so some time in the minor leagues could give him the chance to refine some of his mechanics to get him pitching like he did in 2025.Make sure to visit Pirates OnSI for the latest news, updates, interviews and insight on the Pittsburgh Pirates!Add us as a preferred source on GoogleFollow