Baseball-Reference's Stathead added a feature to search by only All-Star seasons. Presenting the worst seasons by players named to All-Star teams.
Position Players:
1. Reggie Jackson, 1983, -1.8 WAR
2. Alfredo Griffin, 1984, -1.5 WAR
3. Biff Pocoroba, 1978, -1.1 WAR
4. Pete Rose, 1982, -1.1 WAR
5. Mickey Vernon, 1948, -1.0 WAR
Pitching:
1. Derrick Turnbow, 2006, -2.4 WAR
2. Mike Williams, 2003, -1.3 WAR
3. Dick Stigman, 1960, -1.3 WAR
4. Jim Coates, 1960, -1.2 WAR
5. Joe Page, 1946, -1.2 WAR
Turnbow had a breakout season in 2005 and looked good in the first three months of the season. As of June 30 he had 23 saves and an ERA of 3.28. But Turnbow gave up three runs on July 1 without recording an out against the Twins and never looked back. From July 1 to the end of the season: 27 games, 20 2/3 IP, 22 walks, 24 strikeouts, 13.06 ERA. Turnbow always struggled with control and in the second half it just completely fell apart.