Comprehensive training programs for individual sports are often “periodized." That is, they are broken into three or four phases over the year, with each phase concentrating on a particular fitness attribute. For professional sports that utilize weights in their training — which is most these days, each phase has different objectives and each successive phase builds on the previous one.
A year-long baseball weight training program could look like the program outlined below. (Season cut-offs are based on the American baseball season.)