There are lots of great stats out there (like DVOA) which evaluate performance based on situation and competition (vs the really poor gross stats/rankings which are often misleading or worse).
Sharp Football (like Football Outsiders) is a great depot for this. Sharp defines Defense Efficiency in the following way:
"(Play) Success rate is calculated in this manner: A play is successful when it gains at least 40% of yards-to-go on first down, 60% of yards-to-go on second down and 100% of yards-to-go on third or fourth down."
That is a very good way to evaluate play success. Check out the Bucs Defense ranking in terms of Efficiency and Explosive Plays given up from weeks 10 through 17:
PASSING SUCCESS RATE
# 6 overall
Trending during interval # 1
RUSHING SUCCESS RATE
# 2 overall
Trending during interval # 11
EXPLOSIVE PASSING
# 9 overall (ALL SEASON)
Trending during interval # 3
EXPLOSIVE RUSHING
# 3 overall (ALL SEASON)
Trending during interval # 2
