"Phil's fastball velocity was down a touch, the consistency of the breaking ball was a challenge, the change has not come along as well as we had hoped it would," Pirates general manager Neal Huntington said in explaining why Irwin was chosen to make room for Wall. "The injury took a toll, but he's healthy now. We're just not seeing the same sharpness."
Irwin made his Major League debut in an April 17, 2013, start against the Reds at PNC Park, and he also spent a couple days with the Bucs earlier this month, without appearing in a game.
Irwin made 10 appearances, including two starts, this season for Indianapolis and compiled an 8.72 ERA in 21 2/3 innings.
Wall has had a checkered Minor League career, around sporadic big league appearances, since being a second-round pick by the Dodgers in the 2005 First-Year Player Draft.
In 10 seasons divided between starting and relieving, Wall has a Minors record of 41-48 with 35 saves. He posted 28 saves in 2012 with the Dodgers' Triple-A affiliate in Albuquerque.
"He's someone we've tracked for years," Huntington said, "and tried to get a couple of times and were not able to. We're taking a shot in the dark on a guy with a 95-96 mph fastball and a good hard slider. It was an opportunity to add a good arm to our system."
Wall has a Major League ERA of 15.15 in 15 appearances with the 2012-13 Dodgers and the Angels earlier this season.
"Given our needs, we thought Josh is a guy with a good arm who could help us this summer," Huntington summarized.