for players that qualify on fangraphs pre-29 and post-30 Jonathan Lucroy (lol) has the biggest dropoff in WAR per 650 PA Lucroy 7.6 to 1.7 Pujols 7.5 to 1.7 Griffey 6.7 to 1.3 Nomar 6 to 1 Banks 6.6 to 1.9 Andruw Jones 6 to 1.9 some other old-timers mixed in there: Frank Thomas (PIT), George Sisler other notable crash & burn in recent memory: Ryan Howard, Mauer, Wieters, Piazza, Hanley, Darryl Strawberry, Mark Kotsay, Prince Fielder, Matt Kemp, Bobby Abreu, Vlad Sr., Andre Dawson all had 3+ WAR difference in production level after turning 30 Kotsay's is funny because he wasn't even that great younger but then he averaged -1.2 WAR per full season in his 30s