Major League Baseball implemented an experimental, controversial rule Monday to protect catchers, prohibiting baserunners from initiating deliberate collisions at home plate in hopes of preventing concussions and injuries.

Tony Clark, executive director of the Major League Players Association, cautions that the rule will be on an experimental basis only for the 2014 season, particularly after hearing a mixed reaction from veteran catchers.

"I disagree with it,'' Boston Red Sox catcher A.J. Pierznyski told USA TODAY Sports over the weekend. "I understand why they're doing it, but next, they're going to tell us that you can't slide into the guy at second base.

"It's one of those things, as a big-league catcher, I signed up for it. You never want to see guys get hurt, and you never want to see guys go down because of it, but it's part of the game you signed up for.

"There are going to be plays at the plate, late in games, where you need to block the plate and try to keep that guy from scoring, saving save a run that ultimately gets your team into the playoffs.

"And not given that opportunity is unfair. I understand why the rule is made, but I wish there was a better way to go about it.''

The rule, 7.13, was borne in large part after San Francisco Giants All-Star catcher Buster Posey broke his leg in a violent home-plate collision with Marlins outfielder Scott Cousins.

"Our goal is to eliminate the vicious hits, for a baserunner to go and instead of targeting home plate, he's going to target the catcher, like in the Posey case,'' said Joe Torre, MLB's vice president of baseball operations, who has been briefing teams on the collision rule and the expanded use of replay.

The new guidelines still allow runners to initiate contact if the catcher has the ball and is blocking the plate. Runners don't have to slide, but those who do won't be found in violation of the rule.

"He can run into (the catcher), but he can't elbow him, shoulder him,'' Torre said, "and that's where the replay stuff is going to come in.''

The rule also prevents catchers from blocking home plate without possession of the ball. If the catcher impedes the baserunner without the ball, the runner will be automatically safe. And if the baserunner goes out of his way to deliberately initial contact with the catcher, he will be called out.

The home-plate collision will also be subject to instant replay review.

"It puts the umpires in a horrible spot,'' Pierznyski said. They not only have to decide whether the runner is safe or out, but did the catcher block the plate? He's going to have to make a million different decisions.

"I feel sorry for those guys. That's going to be one of the hardest things for those guys. They're going to be put in a really awkward spot.''

Clark understands the mixed feelings and debate with the new rule, addressing it with reporters Monday after meeting with the New York Yankees.