Matheny's plight has others in the close-knit fraternity wondering when a foul tip, errant swing or home-plate collision might sideline them. Or, worse yet, end their career, suddenly a distinct possibility for Matheny.

The Padres' Mike Piazza points to several dents and dings on his mask from where he's been hit in the head this season by either the ball or bat. He considers himself lucky.

"Catchers do receive the brunt of the head injuries. I've had minor vertigo in game situations," said Piazza, who estimates he's had four or five concussions over the years and also got hit in the head by a pitch from Roger Clemens.

"Fortunately for me it hasn't affected my playing, but it could. You get a little lethargic. Your reflexes aren't as quick and you get dazed."

A ball can come off a bat at a greater velocity than a pitched one, and some pitchers throw fastballs approaching 100 mph. Catchers compare the impact to getting punched in the face.

Matheny uses the hockey-style mask preferred by some catchers for its better sight lines, and he was initially convinced it contributed to his concussion. But the Giants enlisted two testing centers to compare the impact resistance of the hockey mask to the traditional catcher's mask — and, so far, they appear to offer similar protection.

Around baseball, opinions vary on the traditional versus hockey mask debate.

"Personally, I don't like the new mask, I don't think it absorbs the blow like the other ones," said Arizona Diamondbacks manager Bob Melvin, a former catcher who had one concussion while in the minors. "I'm concerned with the blows these guys are taking."

Oakland's Jason Kendall uses the old-fashioned version.

"Jason has taken hits on his mask that have bent the mask," Athletics trainer Larry Davis said. "There are a lot of hazards involved. They called catching gear for years the tools of ignorance."

Piazza uses a specially ordered mask that looks like a traditional mask but is heavier.

"It protects me a lot better," he said. "I've never sustained an injury because of a foul tip. You can't protect everything. You'd be like a knight in shining armor."

Home-plate collisions pose another risk to catchers.

Boston's Jason Varitek will never forget a Double-A game when Kevin Polkavich clobbered him in a collision at the plate, bending Varitek's mask. He got the out and stayed in the game, despite seeing spots. He was woozy for a week and had a constant headache, yet never saw a doctor.

The durable Kendall, who's caught more than 140 games in a season seven times in his career, estimates he's had seven concussions in 11 big league seasons. One came when Gary Sheffield barreled into him at home plate in the late '90s at Dodger Stadium.