1
general::
Phrase(s): beat the pants off (of) someone
Go to beat the hell out of someone.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, beat hollow. Win decisively over someone, outdo. For example, When it comes to the Patriots' Day parade, Lexington beats the pants off the neighboring towns, or This beer beats the other brands hollow. Both phrases use beat in the sense of "surpass." Pants off has served as an intensifier since about 1930; the variant dates from about 1775.
American Heritage Idioms