Only one spot exists on the diamond that its not covered by any of the unwritten rules of baseball conduct. It is the Bermuda Triangle no-man's land directly behind the pitcher's mound.

Tonight, as 35,971 fans gasped, a Boston pop-up hung in the air for five seconds, then fell untouched directly in the center of the Baltimore Oriole infield-20 feet behind the mound.

No Oriole player had a decent chance for the tantalizing broken-bat bloop, yet it was the key hit, igniting a seven-run second-inning rally that did all the damage in the 7-5 Red Sox victory.

This game, which brought Boston within half a game of the first place O's, had many other threads:

Fred Lynn capped the seven-run uprising off Mike Flanagan-all of which happened with none on and two out-with his 14th homer, a three-run shot over the center field fence.

O's reliever Sammy Stewart pitched 7 1/3 brilliant innings of shutout relief to give the Birds a chance to draw themselves back into contention.

Billy Smith hit a three-run homer in the second. Lee May doubled home one run in the sixth while Rich Dauer's sacrifice fly knocked in another to cut the Sox margin to a manageable two runs.

In fact, the O's even brought the tying run to the plate after Smith opened the ninth by reaching third on a single and Jim Rice's two run error.

However, as the spirited mobroared, Sox reliever Bill (Soup) Campbell mowed down the last three hitters to finish 2 2/3 innings of shutout work to save Steve Renko's shaky win.

Nevertheless, it is the hallucinatory seven-run inning, and the one-in-a-season play at its center, that every Oriole will ponder as he tries to sleep.

The damage started innocently. Butch Hobson drove a double to right in the gap that Ken Singleton couldn't quite reach. "A lot of outfields gobble that ball up," said Jim Palmer, "but you can't complain. That's just us."

After George Scott walked, Dwight Evans was almost called out on a two-strike checked swing that would have ended the inning.

Evans poked the next pitch down the right field line off the end of the bat for an RBI single.

Then ninth hitter Gary Allenson took a mighty swing, had the bat sawed off in his hands, and watched his mammoth, fatal flare arch over the mound.

"A total fluke," said shortstop Mark Belanger, who came within a stride of catching the ball.

"Whose ball was it?" asked Belanger. "It wasn't anybody's. There is no such play. I've never seen a pop-up hit that low and in just that spot in my whole career. It looked like anybody could get it, but then you realize that maybe nobody could get it. It's just a play that never happens."

Coach Ray Miller visited Flanagan to calm him. But the kettle was bubbling and the Sox ears were perked for action. Jerry Remy and Rick Burleson both lined RBI singles to left for a 4-0 lead.

By now Flanagan was mad. Anyone could see it. "Take this," said Flanagan's first fast ball past Lynn. "And this," said the second. "And this . . . oops," said the third fast ball, which Lynn crushed 415 feet over the center field wall.

Oddly, the Orioles, who have won 23 of 29, viewed this defeat with near-total unconcern. "The way we came back and almost overcame a seven-run deficit was awesome," said Flanagan. "Every pitcher on the staff saw it."

Most important was Stewart, who looks just as valuable as Dennis Martinez did when he was 14-7 in the same jack-of-all trades role in 1977.

"Why start him?" said Weaver, who has watched Stewart look close to intimidating in 96- and 81-pitch long-relief outings against Boston in the last six days."I think he looks pretty darn good where he is."