Here are some 1st half/2nd half stats from mlb98417, a 90M theme league with no WW, DH, AAA, and severe roster restrictions. These are all full-time players.
Note: 1st half stats are exact, 2nd half stats determined by splitting the difference between 1st half and overall stats.
The Steady
1911 Ty Cobb
1st: .408/.465/.511
2nd: .408/.459/.637
1905 Cy Seymour
1st: .383/.405/.551
2nd: .381/.415/.535
Cobb's SLG shot way up, but other than that stable seasons for both players.
The Comeback Kids
1982 Al Oliver
1st: .281/.343/.396
2nd: .385/.419/.546
1897 Billy Hamilton
1st: .280/.381/.332
2nd: .330/.451/.416
Both players underperformed in the 1st half (especially Hamilton, who costs 7.8M). Oliver rebounded to the point where he greatly overperformed in the 2nd half, whereas Hamilton at the very least came close to earning his salary.
The Disappearing Acts
1929 Babe Herman
1st: .382/.436/.570
2nd: .300/.348/.478
1994 Bret Boone
1st: .357/.402/.518
2nd: .309/.344/.402
Both overperformed 1st half, underperformed 2nd half. I wouldn't say by a wide margin in any of the 4 half seasons, but when you compare them side-by-side it seems drastic enough.
I found plenty examples in this league of Steady, Comeback Kids and Disappearing Acts. My unscientific conclusion is that half a season is not such a great sample size.
1/24/2012 2:35 AM (edited)