I tried to compile a list of the best rookie seasons by WAR from Baseball Reference. See my earlier post from August 1, Does Mike Trout Already Have One Of The Top Ten Rookie Seasons Ever? Trout now has a WAR of 8.6. My list would have him 2nd only to Joe Jackson in 1911 (9.0). With almost 40 games left, it seems like he will pass that. He has gained 2.0 in WAR in the last 19 games.
He leads the 2nd best position player in the league, Robinson Cano, by 3.0 (Cano has 5.6). The last time a position player was 3.0 or more better for a whole season than the 2nd best position player was in 2002 when Barry Bonds had 11.6 and Jeff Kent had 6.9.