Ed Delahanty was a 20 year old rookie in 1888 when he joined the Philadelphia Phillies. His first 5 years he averaged only .270 BA.
Then in 1893, he hit for a .368 BA. For the following 10 years of his career, Big Ed consistently hit well above .300 (including .400+
in 3 of 11 seasons).
I calculated his Batting Average for these 11 years, and it is an amazing
.373
TED Z
T206 Reference
.