Everything has a time and a place
For sports that are artistic in nature: i.e. ballet, figure skating, flexibility is important
However in sports that are power speed based, such as baseball, trying to increase flexibility has been shown to REDUCE force outputs (PMID: 11770791), and INCREASE injury risk (PMID: 15076777).
Rather, a baseball athlete should be focusing on improving mobility: good movement patterns and exercises that enhance their ability to move fluidly and unimpaired in actions around a joint--like they move on the field
So much of an athletes success comes down to understanding and executing on the specific needs of THEIR sport
Not someone else’s