My play of the 2000s--Kahlil Hill's 90-yard kickoff return for a touchdown against Michigan State on October 7, 2000. Why? That was the play that very likely saved Kirk Ferentz's job.
The Iowa offense was struggling that day. Michigan State had just scored to go up 16-7 late in the third quarter. Immediately after the MSU score you could feel the air rush out of the stadium as no one in the stands or on the field felt that Iowa could score enough to overcome that lead--then Kahlil Hill returns the kickoff for a touchdown, and it is a new game--a game that Iowa ekes out 21-16.
Iowa was 1-15 at that point in the Ferentz era. Without that kickoff return we would have lost to Michigan State. After the Michigan State game we got blown out against Illinois and Ohio State. Without the win against Michigan State, I doubt we would have played Wisconsin close the week after OSU. I doubt we would have won in double overtime against Penn State the following week. And, not having beaten Michigan State or Penn State, I doubt we would have beaten Northwestern. Assuming that is the case, Ferentz would have been 1-10 in 1999, and 0-12 in 2000. My guess is that would have been the end of the Ferentz era.
Sometimes when you are struggling, the difference between winning and losing, between building momentum and losing your team, isn't that great and may hinge on a single play. I would argue that one play was critical to Iowa turning the corner under Kirk Ferentz and thus all of the success we have enjoyed over the last ten years might not have happened without this single play--when Kahlil Hill saved the day, the season, and the Kirk Ferentz era by running a kickoff back for a touchdown against Michigan State. And thus, for me, since all of our success harkens back to that one single play, that play is my play of the decade.