The reason for the question are changes in the rules on rosin bag usage from when I pitched in college over 40 years ago. When I pitched I had my own rosin bag and took it to the dugout when we were batting. From what I have read it seems that in MLB the league/umpires supply the rosin bag and it is left on the mound for the entire game. What are the rules for high school, 14's, 13's, and the lower ages? I have not noticed rosin usage in the lower ages.