He kind of was garbage last year, and apparently he acted like a punk and didn't like the new management in Texas. He refused to show up for certain assignments from the team and was just generally combative with what the team wanted him to do. The Texas outfield was also crowded with Deshields Jr and Mazara needing playing time, so it made sense for them to ship Martin out.
I sure am glad all of this is happening though! Annnnnd hopefully his hamstring issue is just a cramp =.=.