BOSTON — Someone once said that baseball is a game of inches. The difference between a strike and a hit, the difference between a stolen base and a game-ending out.

Or the difference between a frustrating hitting slump that has fans trying to ship you out of town and a towering grand slam to kick off a rout.

Such was the case for Coco Crisp. Sometime around the middle of May, he changed his batting stance a bit — for the worse.

Over the next 14 games, he was a dismal 8-for-51 (.157), and radio talk shows were filled with chatter either making excuses for the center fielder, saying he must still be bothered by the broken left ring finger that plagued him throughout last season, or those who flat out wanted him out of town.

But Red Sox hitting coach Dave Magadan noticed that Crisp was bending his knees too much in his stance. Boston great Jim Rice noticed the same thing, and passed along his observation, as well.

So Crisp did a lot of work with Magadan in the cage, pulling himself more upright at the plate.

The difference in his stance was likely inches.

But it has made all the difference in the world.

Since straightening up, Crisp has been the Sox’ hottest hitter over the last three weeks, and is batting a glittering .431 over his last 16 games.

He provided the early fireworks in a largely yawn-inducing game last night. With two runs already on the board for Boston, the bases still loaded and just one out in the first inning, Crisp got all of Devil Rays starter J.P. Howell’s 1-0 offering, sending it over the Green Monster. The ball hit the Coke bottle and bounced back onto the field for the second grand slam of his career.

His first came on July 27, 2004, against the Tigers when he was a member of the Indians.

When he was at the plate, Crisp wanted to “just get the ball in the air. I was trying to get it in the outfield somewhere. (But) as soon as I hit it, I knew I got it. (Howell) left it right down the middle of the plate.”

The stage was set for Crisp to get another grand slam in the third when he again came up with the bases loaded and one out. He didn’t go yard, but he did record his fifth RBI of the game by drawing a walk that plated Manny Ramirez.

The five runs batted in tied his career-high; his other five-RBI game came in the game in which he got his first grand slam, nearly three years ago.

In all, Crisp went 2-for-5 last night, extending his hitting streak to seven games and raising his batting average to .265.

Since being at a low of .221 after an 0-for-4 performance against Colorado on June 13, Crisp has hit safely in 15 games (25-for-58), with three doubles, Wednesday’s leadoff triple, four home runs, 11 RBI and 12 runs scored.

During his current seven-game hitting streak, he is batting .370. It has continued despite missing four games with a thumb injury suffered last Wednesday in Seattle.

“That’s why we tried not to play him until he did feel like he could swing the bat,” manager Terry Francona said. “We wanted his hands to feel OK so he could swing the bat. He certainly showed that he is (feeling fine). The ball’s coming off his bat both ways. He’s been aggressive at the plate, and he’s swinging with some oomph without trying too hard.”

Crisp’s offense is catching up to his defense, which has been stellar all season. Last night, he added to his collection of outstanding catches, making an over-the-shoulder, warning-track grab of Jonny Gomes’ fly ball in the sixth inning.

Over 71 starts in center field for Boston, Crisp has made just one error, which came last July.

smanza@projo.com