Yoshi: What Happened?

Today against the Athletics, Rangers reliever Yoshinori Tateyama came in with the bases loaded and promptly gave up a grand slam. His last two outings have been really bad: 1 out, 5 hits, 2 homers allowed, 6 ER. It hasn't been all bad though, in fact, Yoshi has been quite good. Even after recent struggles his ERA is 4.29 (with a 2-0 record), 40 strikeouts (with just 10 walks), and a WHIP of 1.024. His WAR is still .2, and with a salary of $800,000, his WASP (War and Salary Per) is 4,000 (which isn't all that great, but by no means horrible). The side armer has clearly been struggling with command as of late (something that was pinpoint when he first came up), and I think this is a much bigger issue than "the league figuring him out" (as one member of Twitter suggested).