As you might well expect, we have a good bit more of the same in terms of first-half performance peaks in the 1930s as was the case in the 1920s. Remember, the "Top 300" here is sorted using descending order of OPS+...here we go:
After being absent from the top in 1930-31, Jimmie Foxx returned with a vengeance in 1932-33, featuring first half-performances that both rank in the Top 20 all-time. (1932 was the year in which Double-X challenged the Babe's HR record and wound up with 58.) As was also the case with Chuck Klein, Ruth added two more "Top 300" first halves in 1932-33, though as you can see they are much closer to the bottom end of the list than was the case in 1930-31.
We telescope four years (1934-37) into this list, which features three first-half performances spikes for Lou Gehrig (missing out only in 1935). We see Joe Medwick and Hank Greenberg for the first time, and witness a remarkable first half from 23-year-old Arky Vaughan, who just misses joining Medwick as a .400+ hitter, while compiling an OBP (.502) topped only by Babe Ruth in 1930-31. The depth of Yankee talent at this point in the 30s is embodied by George Selkirk, used in a strict platoon by manager Joe McCarthy.
Jimmie Foxx has another 50 HR season in 1938, but 1939 would be his last appearance on our first-half leaderboard. The Reds' Ival Goodman was on fire in the first half of 1938, which makes him the most obscure player to appear on this list during the 1930s.
Facts from the numbers: 20 of the 34 hitters in the first-half "Top 300" hit 20 or more HRs, while only two of them hit .400 or higher. Three players had OBPs higher than .500, but 20 had an OBP of .450 or higher. Sixteen had SLGs higher than .700, and all 34 had an OPS of 1.000 or higher.