UFC 2009 Undisputed
30 Achievements
1,000
Xbox 360
World Class Grappler
Win by Submission using no striking against a COM UFC Fighter in Exhibition or Career Mode.
30
How to unlock the World Class Grappler achievement in UFC 2009 Undisputed - Definitive Guide
You cannot strike an opponent on the ground once you have them on the ground. Simply grab a good grappler (toggle stats with in the select fighter menu) and body slam them until you get them weak. Rotate your stick and click it a few times to get into a good submission move and rotate to break their body parts. Should unlock after he submits.
If your going for "Trophy Collector" you'll most likely be able to get this using the strategy there.