From MLB Power Pros Wiki

Walk-Off Hitter gives a hitting ability boost in walk-off situations. When acquired, the on-screen message will read "Now a Clutch Hitter"

Areas Obtained:

• Secrets of Hitting book
• Insurance Salesman Random Event
• Quitting your waitering job

Acquisition in My Life Mode (2008)

• Gain Walk-Off Hitter experience by getting a Walk-Off hit