Ray Chapman

Jeff Suntala
Wikipedia - "Raymond Johnson Chapman (January 15, 1891 – August 17, 1920) was an American baseball player, spending his entire career as a shortstop for Cleveland. He is the second of only two Major League Baseball players to have died as a result of an injury received in a game (the first was Mike 'Doc' Powers in 1909); Chapman was hit in the head by a pitch thrown by Yankees pitcher Carl Mays. His death led Major League Baseball to establish a rule requiring umpires to replace the ball whenever it became dirty. His death was also one of the examples used to emphasize the need for wearing batting helmets (although the rule was not adopted until over thirty years later). His death was partially the reason MLB banned the spitball after the season."
Wikipedia, Baseball Reference