Through 2019. Ranked by WAR (baseball-reference+Clay Davenport, the best WAR number that exists).
1. 2001 Barry Bonds 12.1
2. 2002 Barry Bonds 11.6
3. 2009 Barry Bonds 10.9
4. 2004 Barry Bonds 10,8
5. 1993 Barry Bonds 10.3
6. 1996 Barry Bonds 9.75
7. 2003 Barry Bonds 9.6
8. 1998 Barry Bonds 9.1
9. 1997 Barry Bonds 8.5
10. 1995 Barry Bonds 8.2
11. 2000 Barry Bonds 8.1
12. 1989 Kevin Mitchell 7.9
13. 1994 Barry Bonds 6.6
14. 1961 Orlando Cepeda 6.2
15. 1951 Monte Irvin 6
16. 1963 Willie McCovey 5.95
17. 1917 George Burns 5.9
18. 1900 Kip Selbach 5.65
19. 2012 Melky Cabrera 5.3
20. 1920 George Burns 4.65
21. 1918 George Burns 4.65
22. 1990 Kevin Mitchell 4.55
23. 1919 George Burns 4.55
21. 1918 George Burns 4.65
22. 1990 Kevin Mitchell 4.55
23. 1919 George Burns 4.55
24. 1886 Jim O’Rourke 4.55
25. 2006 Barry Bonds 4.35
26. 2007 Barry Bonds 4.25
27. 1999 Barry Bonds 4.2
28. 1944 Ducky Medwick 4.1
29. 1960 Orlando Cepeda 4.05
30. 1883 Pat Gillespie 4.05
31. 1948 Whitey Lockman 4
30. 1883 Pat Gillespie 4.05
31. 1948 Whitey Lockman 4
32. 1953 Monte Irvin 3.85
33. 1971 Ken Henderson 3.8
34. 1970 Ken Henderson 3.8
35. 1984 Jeffrey Leonard 3.65
34. 1970 Ken Henderson 3.8
35. 1984 Jeffrey Leonard 3.65
36. 2005 Moises Alou 3.55
37. 1935 Jo Jo Moore 3.55
37. 1935 Jo Jo Moore 3.55
38. 1936 Jo Jo Moore 3.4
39. 1934 Jo Jo Moore 3.3
39. 1934 Jo Jo Moore 3.3
40. 1975 Gary Matthews 3.2
41. 1991 Kevin Mitchell 3.1
41. 1991 Kevin Mitchell 3.1
44. 1885 Jim O’Rourke 3
45. 1974 Gary Matthews 2.9
46. 2010 Pat Burrell 2.85
47. 1973 Gary Matthews 2.85
48. 1903 Sam Mertes 2.85
49. 1983 Jeffrey Leonard 2.75
50. 1891 George Gore 2.75
And the worst left field season in Giants history...1943 -2.45 Buster Maynard
