Here's a look at the transactions this week that had the most significant fantasy impact.
Carlos Lee, 1B - placed on the 15-day DL (left hamstring)
Brett Wallace, 1B - recalled from Triple-A Oklahoma City
Impact: The last few seasons, Lee has seen his offence tail off considerably. While he's no longer the 30-homer, 100-RBI threat that he once was, he's still a pretty decent hitter. Through his first 49 games this year, he has hit .297 with four home runs and 23 RBI. He'll be sidelined for at least a couple of weeks with a strained left hamstring. In the meantime, Houston will give Brett Wallace another chance to show he can handle major league pitching. His career numbers coming into this season aren't pretty, especially for a first baseman. Wallace brings a mediocre career batting average of .248 into the 2012 season, and he's managed to hit just seven home runs and collect 42 RBI in 480 career at-bats. He has hit well enough throughout his minor league career, so the potential is clearly there.
Jaime Garcia, LHP - placed on the 15-day DL (left shoulder)
Fernando Salas, RHP - recalled from Triple-A Memphis
Impact: Garcia will miss at least a couple of weeks as he recovers from a strained left shoulder. The 25-year-old lefty had a couple of good seasons in 2010 and 2011, as he went a combined 26-15 with a 3.17 ERA over 60 starts. He hasn't been quite as good this year, as his ERA has ballooned to 4.48. St. Louis has yet to announce who will fill Garcia's turn in the rotation Sunday. Salas led the Cards in saves a year ago with 24, but pitched terribly in 18 games this year before being demoted in late May. He returns to an ugly 6.32 ERA and a horrible 2.04 WHIP, though he did strike out 21 batters in just 15.2 innings.
Jason Bay, OF - activated from the 15-day DL
Chris Young, RHP - placed on the paternity leave list
Impact: Bay will attempt to return to form after missing more than a month with a fractured rib on his left side. After back-to-back poor seasons in 2010 and 2011, Bay wasn't doing much better this year before the injury, hitting just .240 with three home runs and five RBI through 15 games. While Bay isn't likely to return to his 30-homer, 100-RBI days, Citi Field's more hitter-friendly dimensions should help him improve his numbers from the last couple years. His health always seems to be an issue these days, however, as he's spent significant time on the DL in recent years. Young will spend some time on the paternity list after having his contract selected from Triple-A Buffalo on Wednesday. Injuries limited him to just eight starts over the 2010 and 2011 seasons, though he pitched well in those starts, posting an 1.43 ERA. He should return to the rotation when he rejoins the team.
Huston Street, RHP - activated from the 15-day DL
Miles Mikolas, RHP - optioned to Triple-A Tucson
Impact: Street returns to his closing duties after missing a month with a strained right shoulder. He was dominant before the injury, converting all four of his save opportunities while striking out 13 batters in just 9.2 innings. He returns to a great 0.93 ERA and a stellar 0.52 WHIP. Dale Thayer was Street's replacement the last month and had been unscored upon in his first 10 appearances of the season before a couple of bad outings ruined his numbers. He'll return to a middle-relief role after converting all five of his save opportunities. Mikolas has an 3.29 ERA through 13 relief appearances and had not been scored upon in his last eight games. He should get another look later this season.
Vance Worley, RHP - activated from the 15-day DL
Erik Kratz, C - optioned to Triple-A Lehigh Valley
Impact: After an impressive 2011 season, Worley was off to a good start this year before being shut down for almost a month with inflammation in his right elbow. He put himself on the fantasy radar last season by going 11-3 with a 3.01 ERA and 119 strikeouts in 131.2 innings with the Phillies. This year, he was 3-2 with a 3.07 ERA and 45 strikeouts in 44 innings over seven starts before he hit the DL in mid-May. He should be safe to add in all fantasy formats. Kratz was 1-for-4 with a home run in four games as the Phillies third-string catcher.
Derek Holland, LHP - placed on the 15-day DL (left shoulder)
Tanner Scheppers, RHP - contract purchased from Triple-A Round Rock
Impact: After seeing his season ERA jump from 4.05 to 5.10 over his last couple of starts, Holland will take some time off to rest his overworked left shoulder. The 25-year-old left-hander was a key contributor in Texas' playoff run last season, as he went 16-5 with a 3.95 ERA. Alexi Ogando now moves from the bullpen to the rotation, where he pitched fairly well last season. Ogando was 13-8 with a 3.51 ERA in 169 innings in 2011 and has pitched even better this year while working in relief. Scheppers will work out of the bullpen and isn't likely to be used in many high-leverage situations for the time being.
Desmond Jennings, OF - activated from the 15-day DL
Rich Thompson, OF - optioned to Triple-A Durham
Impact: The top of the Rays' lineup got a boost Tuesday when the speedy Jennings returned to action. He had been out a few weeks with an injury to his left knee, but looked sharp as he collected three hits in his first two games back. He returned to a .265 average with three home runs, 11 RBI, 20 runs scored and eight stolen bases in 31 games. As expected, Ben Zobrist has moved in from outfield to man second base. With Sean Rodriguez playing every day at either third base or shortstop, Elliot Johnson and Will Rhymes will share playing time at the remaining infield position, at least until Evan Longoria and Jeff Keppinger return from the DL. Thompson collected just one hit in 16 at-bats, but could be called upon again the next time the Rays need another outfielder.
Andy Dirks, OF - placed on the 15-day DL (right Achilles)
Matt Young, OF - called up from Triple-A Toledo
Impact: Dirks was swinging a hot bat as the Tigers' primary left fielder before being shelved with right Achilles' tendinitis. In 37 games, he has posted a healthy batting average of .328 with four homers, 16 RBI and 24 runs scored. Young figures to split the left-field duties with Don Kelly, who has struggled mightily with the bat this season. Young probably won't fare much better based on his minor league numbers, so it's fortunate that Dirks is expected to return to action when he becomes eligible June 15.
Alex Avila, C - placed on the 15-day DL (right hamstring)
Bryan Holaday, C - contract purchased from Triple-A Toledo
Impact: A strained right hamstring will keep Avila sidelined for at least a couple weeks. The 25-year-old catcher put together a nice 2011 campaign as he hit .295 with 19 home runs and 82 RBI. His numbers this year haven't been quite as impressive, though he's still done pretty well for a catcher (.250, five home runs, 20 RBI in 44 games). Holaday will split time behind the plate with Gerald Laird, though neither player is worth owning in most leagues.