Interesting, hadn't even thought of that.
What are the top averages through the ~first 40 games of a season?
Researched this for a 60 game sample actually earlier this month, here’s what I came up with:
First 60 games of team, memorable seasons batting:
-Ty Cobb, 1911: .443/.493/.668
-Darin Erstad, 2000: .384/.446/.585
-Carney Lansford, 1988: .384/.432/.516
-Jason Giambi, 2001: .359/.496/.689
-Larry Walker, 1997: .417(!!)/.514/.787
-John Kurk, 1992: .369/.448/.491
-Wade Boggs, 1986: .379/.491/.530
-Rico Carty, 1970: .395/.484/.688
-Chipper Jones, 2008: .409/.498/.657
-Cody Bellinger, 2019: .376/.462/
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Pitching seasons through 60 team games:
-Don Drysdale, 1968: 1.31 ERA, through 110.1 IP, .198/.250/.256 against.
-Pedro Martinez, 2000: 0.95 ERA through 85.1 IP, .152/.213/.199 against.
-Bobby Shantz, 1952: 1.59 ERA, through 136 IP, .196/.246/.272 against.
-Juan Marichal, 1966: 1.73 ERA through 120 IP, .183/.220/.251 against.
-Lefty Grove, 1931: 1.77 ERA (AL through full season was 4.38), through 127.0 IP, .208/.266/.309 against.