<Li> There is an automatic ejection for maliciously running into a defender who is trying to tag a runner or execute a force out . An automatic double play may also be called if a player slides into a base in an attempt to take out the defensive player who is trying to throw the ball to complete a double play . </Li> <Li> In televised games and in tournament games, instant replay may be used to determine if a slide was malicious . </Li> <P> Though a wood bat is legal in NCAA competition, players overwhelmingly prefer and use a metal bat . The metal bat was implemented in college baseball in 1975 . Use of a metal bat is somewhat controversial . Supporters of an aluminum or composite bat note that it can increase offensive performance, as the speed of a ball off a metal bat is generally faster than off a wood bat . Those against metal, and for wood, argue that a metal bat is not safe to use, and that a metal bat doesn't prepare players for the next level, as professional baseball uses a wood bat exclusively . In the 2011 season the NCAA changed the requirements for a metal bat, reducing the maximum allowed exit speed in a way that is said to produce a feeling more like a wood bat . As a result, in 2011 there was a drop - off in overall "long" drives or home runs relative to past years . </P> <P> All players resident in the U.S. and its territories, plus Canada, are eligible to be selected in Major League Baseball's Rule 4 Draft upon graduating from high school . However, once a player enrolls in a four - year college or university, he is not allowed to be drafted (or re-drafted) until completing three years of school or reaching age 21, whichever comes first . By contrast, players who enroll in junior colleges (i.e., two - year institutions) are eligible for selection at any time . The Rule 4 Draft of eligible college and high school players consists of 40 rounds . Despite MLB's draft being considerably longer than that of the NFL or NBA, only about 9.1% of all NCAA senior baseball players are drafted by an MLB team . </P>

When did college baseball switch to aluminum bats