Stewart, 26, was once a hot prospect and is already pretty well traveled: the Reds selected him in the third round of the 2008 draft, then the Blue Jays acquired him in the deal that sent Scott Rolen to Cincinnati; Toronto traded him to the White Sox in the three-team trade that sent Colby Rasmus to the Blue Jays; the Red Sox acquired him in the deal that sent Kevin Youkilis to Chicago, and now he's in Pittsburgh.
According to Sox Prospects, the scouting report on him is "Sinker/slider pitcher that has been used both as a starter and a reliever in his brief major league career. Fastball sits in the low-90s and induces a lot of grounders. Mid-80s slider is currently his best pitch. Also mixes in a changeup that needs more development. Doesn't walk many batters. Mediocre strikeout rate. Has allowed home runs at a much higher rate in the majors than the minors."
The righty went 1-4 with a 8.58 ERA in 20 appearances for the White & Red Sox in 2012 and was 3-5 with a 3.94 ERA in 11 starts for the Triple-A Pawtucket Sox. In his career, he's 3-10 with a 6.82 ERA in 33 games, 103 IP of work, 64 K and 2.2 HR/nine innings. He has an option left, so spring training isn't do-or-die for him.
Both of the guys the FO traded for from Kansas City, Mazzaro and Robinson, were also DFA'ed.
RHP Mazzaro, 26, is another journeyman who has spent four seasons in the show with 15-21/5.22 slash compiled in 66 appearances, including 45 starts. He's a wild child, averaging nearly 4 walks per game with a low 5.5 K per nine rate. He put up a 4-3/5.73 ERA in 44 IP for the Royals in 2012 during six starts and 12 bullpen outings.
He made the record books in May, 2011, when he became the first player in MLB history to allow fourteen runs in less than three innings against the Indians, though he did rebound after that melt-down, with a 4.15 ERA the rest of the season. The righty was a 3rd round pick of the As in 2005.
Mazzaro is a good change of scenery candidate, although his peripherals don't indicate very much upside beyond MLB long man/spot starter. He throws a 91 MPH sinker as his bread-and-butter, and gets in the low-to-mid 40% of his outs in the dirt. Mazzaro and Stewart both indicate a bit of a shift in Pirate thinking; now they're not only going for the big trees with power arms, but adding sinker-ball types to the mix.
1B Clint Robinson, 27, made his major league debut with the Royals last season, (it was at PNC Park on June 8th when the lefty struck out against Hanny to close out the Bucs 4-2 win) but only got four at-bats in the show, K'ing twice. He spent the bulk of the season at Omaha in the hitter heaven of the PCL, where he batted .309 in his two AAA seasons with an OPB of .396, a K rate of 14%, 72 doubles and 36 HR, showing some discipline and pop.
He's the most interesting of the trio; maybe the Bucs think that Garrett Jones-type lightning can strike twice (and if so, the irony would be Robinson could replace Jones in 2014). John Sickels said of him going into 2012 "I know he's old, but I think he can hit, and would be a useable DH/1B bat for someone in the majors." The FO was looking for a bat off the bench, and at worst shored up a position that's thin at the upper levels of the organization.
The Bucs sent a couple of DSL arms to the Royals for the pair. Rico, 19, was awful while Santos, 21, has a three year slash of 8-4/2.51 with 10 strikeouts and three walks per nine and a good ground ball rate, but is a little long in the tooth for his level.
They also had to clear a couple of spots on the 40-man roster, and did so by DFA'ing 1B Matt Hague and IF Yamaico Navarro. Now the roster is filled, so the Bucs look like they're going to pass on the Rule 5 Draft this year.
While they are edge-of-the-roster moves, the FO could possibly be reinforcing themselves for arbitration. Mazzaro in particular and Stewart join the small posse of arms the Pirates have recently signed, making them possible internal replacements if Jeff Karstens, as rumored, is non-tendered. We'll see how that plays out by November 30th.