spot, that was my thought at one point too, but I changed my mind after additional research and some information from others on TT.
Some documents from the USTA use language that would seem to imply it is the "current dynamic rating", i.e. the result after the dynamic rating from the match is averaged with the prior dynamic ratings. For example:
"If a player’s dynamics reaches the DQ Zone three times (each dynamic that reaches the DQ Zone is called a strike) then the player strikes out of the level and is moved to the next highest level."
"24. What is a strike and how do I get one? Each time a player’s dynamic rating exceeds the maximum tolerance for the level, he or she automatically earns a “strike.”"
But neither of these is perfectly clear that it is in fact the averaged dynamic rating and not the match dynamic rating, the language is a bit ambiguous.
Then there is this TT thread where the subject is discussed. http://tt.tennis-warehouse.com/showthread.php?t=420009
In it J_R_B clearly states that it is the individual match rating that is used. We also know from this thread and others that 6-0,6-0 wins can count as strikes and while there is evidence now that 6-0,6-0 matches are counted for rating purposes, we know they weren't in the past and if they weren't used and it is the averaged dynamic rating that results in a strike, that wouldn't make sense.
Last, because we know the USTA does try to avoid making it so players can game the system, it wouldn't make any sense to use the averaged dynamic rating for strikes for the very reason that someone could throw a match to get their rating low so they could win their next match and not get a strike.
But, I could be wrong.