Shares of Under Armour Inc (NYSE: UA)(NYSE: UAA) were up as much as 11.9% on Friday, Dec. 15. As of 1:35 p.m. EST, they've cooled off a bit, but are still up 8.7% (UA) and 7.7% (UAA). This big jump was primarily caused by a note released today by Stifel analyst Jim Duffy, who upgraded his rating on Under Armour from "hold" to "buy." Duffy also increased his price target to $17, $5 higher than the prior $12 target. Duffy's vote of confidence was multi-pronged.