Implementation is immediate. For the Mariners, that means their Cactus League opener at 12:05 p.m. Pacific time Thursday against San Diego at Peoria Stadium.
Let's just say there's still a few devils in the details.
The basics are this: A runner can't deviate from his direct path to the plate in order to initiate contact, and a catcher can't block that path unless in possession of the ball.
Seems simple enough.
But Mariners catcher John Buck was among those who helped craft the rule, and he's quick to suggest "it's going to take some time to get everybody used to its interpretation."
Buck said the rule guarantees the runner a path to the plate unless a throw carries a catcher into that path. But ... Buck says the rule, as written, permits a catcher to straddle the plate while awaiting a throw. "There's still a lane (between the catcher's legs)," he said. "That's a clear lane to the plate, but that seems kind of dangerous to legs and knees, too."
Manager Lloyd McClendon, a former catcher, doesn't see a big difference.
"You can't change direction to go after the catcher," he said. "I think that's good. The health of the player is what's important, and I think that part of the rule will be real good.
"Other than that, I don't think much has changed."
The rule also seeks to protect the runner. Catchers won't be permitted to throw out a leg at the last instant to block a runner. Nor can they simply position themselves with their shinguards blocking the plate.
"I don't think it's going to be too much (of an adjustment)," catcher Mike Zunino said. "We might just need to move up a few inches to give the runner (a lane to) home plate. Go from there.
"I still think there are going to be bang-bang plays at the plate. It's going to be more work for umpires. The new rule is big on interpretation. That's what it comes down to."
So what contact is permissible?
"The way they explained it to us," Buck said, "if the runner's shin or their butt hits the ground before contact with the catcher, that would be a gauge for the umpire on whether it's a slide.
"That's (acceptable) contact. That's not coming in maliciously. That's part of the game."
Buck said plans are in the works for players and club personnel to receive specific instruction either through video presentations or by visits from Major League Baseball officials.
"The first two or three plays are going to be heavily scrutinized, obviously," he said. "But I think they're moving toward making it better and protecting catchers."
Buck said he initially opposed the rule but changed his mind after hearing St. Louis manager Mike Matheny, a former catcher, argue for its implementation.
"He was a guy who would lay down on the plate to stop a run," Buck said. "He wanted contact. But hearing some of the life circumstances he's now dealing with changed my mind a little bit."
Specifically, Buck pointed to a growing awareness, in baseball and all sports, regarding the potential consequences of suffering a concussion ... and the cumulative effect of doing so repeatedly. "It takes one play, literally, to end your career," he said. "Maybe end somebody's life, really. So if there are just one or two collisions that didn't have to happen ... the more you get hit, the more bruising on the brain.
"It would be irresponsible not to try to change that a little bit. At the same time, you don't want to change the outcome of the game. You just can't let a runner have home plate. It's the most exciting play in the game."
For now, though, the rule is likely to evolve through application.
"I think it's a good rule," Zunino said. "They're trying to keep everybody safe, and we have to adjust. Hopefully, both ends abide by it, and there are not many confrontational calls about it."
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