A former high school jock is thrust into duty to save his high school reunion after a prank turns his classmates into the living dead.

Well ... the rescue of the ex-girlfriend seems pretty central to the idea?

"After a viral outbreak turns the attendees of a 10 year reunion into ravenous zombies, a down-on-his-luck ex-jock turned shoe-salesman battles?the living dead to rescue?a group of survivors (and his high-school sweetheart) trapped in?the gym."

Maybe a LITTLE wordy, but I think clearer and provides more of the hook -- or at least hints at the themes of redemption and reclaiming former glory?

Substitute 'viral outbreak' for 'chemical explosion' or 'miscast spell', whatever happens. I think 'prank' calls for specificity, and weighs down the logline in the wrong place (because the reader is curious about the nature of the prank). I'd suggest keeping that bit a little vaguer (leave it for the script - just describe the outcome of the prank) and get the logline to the meat and potatoes of the story quicker.

With a little more information, I'm more interested in the story, for sure, and can see?the script's potential. (Who are the survivors? Did they not drink the tainted punch that turned everyone into zombies because they're the members of his AA group, or worse ... the nerds he used to pick on? Maybe he busted his knee and couldn't play?basketball anymore - a cliche, I know - but dragging the ex-jock to the part of the school that resulted in the current trajectory of his life is a great way to build 'the cave' in the second act).

As for 'who would want to play this part' - in a story of arrested development and the quest for former glory, I can see tons of actors who'd go for that. My first thought was Chris Pratt (but fat Chris Pratt from Parks & Rec).

Anyway ... good luck with the logline and/or script.