Baseball Card Adventures by Dan Gutman
This series actually combines elements from the first two in the list – it has both a time-travel and a sports motif.
Joe Stoshak, a sports-loving 12-year-old boy, is able to use baseball cards to travel back in time and meet different baseball players at pivotal points in their careers. Although some of the players are likely to be unfamiliar to kids (Honus Wagner, Ray Chapman), others are names just about every child will be familiar with (Babe Ruth, Jackie Robinson).
These books are somewhat longer than the Time Warp Trio and Jersey series, coming in a little over 150 pages each, and the humor is a bit more restrained than in the former, but they are highly entertaining for any boy interested in baseball or history – and are likely to make any baseball fan a little bit more into and aware of the history that lies behind his favorite sport.
The books are available new, in paperpack, hardcover or digital format, and used copies are readily available. Here's a link to the Jackie & Me book on Amazon.