MLB's Rules Committee has voted to outlaw collisions at home plate. The next step in the process is to gain approval from the players, which could lead to the change being implemented for the 2014 season. The players are expected to approve it, but even if they don't, MLB could implement the change unilaterally for 2015.
There isn't yet a formally written rule, so the expect specifics of it (and the penalties for players who break the rule) are not yet available, but the gist of it is that base runners will no longer be allowed to initiate contact with the catcher on plays at the plate, and catchers will no longer be allowed to block the base path. Home plate will now (basically) be treated the same as any other base, in terms of the rules governing base running plays there.
The rise in our collective understanding of concussions is one factor that's led to this change, which was also spurred on by a number of high-profile collisions, some of which knocked players out for months, including Buster Posey of the San Francisco Giants back in 2011 (when he was reigning NL Rookie of the Year):
Posey missed the rest of the 2011 season with a fractured ankle and ligament damage. Fortunately he was able to make a full recovery (as evidence by his winning the 2012 NL MVP Award).
"He just needs a second, to let all the cobwebs come out."
That's what you hear at the 0:41 mark and it shows how so many still respond to plays like that, downplaying its possible severity. Marson did in fact finish out the inning, but was then pulled from the game. He wound up on the DL with a concussion and a cervical neck strain.
The straw that broke the camel's back may have been this collision during Game 5 of this year's ALCS, when millions and millions were watching:
Major League catchers past and present have been divided on the issue. Mike Matheny, current manager of the St. Louis Cardinals, and former MLB catcher whose career was cut short by concussions, was against banning collisions at the plate when he was a player, and both Marson and Avila both described the plays that injured them as "part of the game," but Matheny changed his mind after he became a manager.
"What I've personally witnessed was enough for me to change my mind. It actually took me a little longer 'til I got to the realization of the risk we're putting these guys in -- and the runner, too... This isn't a collision sport. There's enough of a physical grind with guys being out there for 162 games."
Other levels of American baseball as well as leagues around the world have already outlawed the home plate collision, and I'm happy to see MLB now taking this step to protect its players too.