This is a slightly annoying trophy to grind out. It will take you a lot longer than you think. However it'll help you on the way to
I found the best way to do this is to take Ryu into Versus mode against a Zangief on the easiest difficulty, with 7 rounds.
Then Beat down zangief til he's almost dead. I found the life bar should be just under 3 of the victory marks that are below the life bar, but you should experiment with what makes you comfortable. Then let Zangief beat you up.
Once the green ultra bar in the bottom leff is full you want to do your ultra combo. If you chose Metsu Hadoken that's two quarter circles forward and all three punch buttons (map the three punch button to a face button of the controller if you want this to be easier).
You will get a flashy screen if this kills him and an U instead of a V
Get 50 of these and you are done with this trophy.