George Foster hit a grand slam in a six-run, fight-marred sixth inning as the Mets defeated the Los Angeles Dodgers, 8-1, last night in New York behind Ron Darling's five-hitter.

The Mets sent nine men to the plate in the sixth inning before the Dodgers could get an out. After Foster's grand slam, the 13th of his career, reliever Tom Niedenfuer hit Ray Knight in the elbow with a pitch.

Knight charged the mound, tackled Niedenfuer and punched him several times in the back as both benches and bullpens emptied. The field was cleared after several minutes, and neither Knight nor Niedenfuer was ejected.

The fight was the second one of the night. Before the game, teammates Greg Brock and Steve Sax scuffled in the Dodgers dugout. Later, Brock said: "Sure, we had a disagreement, but it wasn't a fight."

Darling (6-0) matched the Mets club record for consecutive winning decisions at the start of a season in his first complete game of the year. Bob Welch (3-4) lost to the Mets for the first time since July 12, 1982, a span of six victories.

Right fielder Darryl Strawberry was taken out of the Mets' starting lineup with a strained left thumb and the team listed his status for the rest of the three-game Dodgers series as "day to day."

Darling struck out 12, tying a career high, and walked two.

*Braves 6, Pirates 2: Atlanta's Terry Harper hit a grand slam with two outs in the 12th inning and a season-low crowd in Pittsburgh of 2,830 watched the Pirates drop their sixth straight, their longest losing streak of the season. The Braves won their third in a row.

Atlanta loaded the bases when Rafael Ramirez walked, Dale Murphy singled and Bob Horner was intentionally walked. Harper, who entered the game on defense in the 10th, hit a 1-1 pitch into the left field seats for his fourth homer of the season.

*Reds 5, Cubs 4: Dave Parker had four singles, including one off the right field wall to drive in the go-ahead run, to help Cincinnati get the win in Chicago.

The Reds, who have won five of their last six, took advantage of three errors to score two unearned runs and give Tom Browning (2-4) the victory.

Dave Concepcion walked with one out in the fifth, stole second and scored when Parker singled off the right field wall to end a 2-2 tie. Davey Lopes put the Cubs ahead in the first with his second homer of the season but the Reds tied it in the second on Eric Davis' triple and Bo Diaz's fly.

*Expos 5, Padres 4: Hubie Brooks' groundout drove in Mitch Webster from third base with the tie-breaking run in the seventh inning and the Expos won in Montreal.

Webster, who had three hits, led off the seventh by reaching base on an error by San Diego reliever Tim Stoddard (1-2). Webster stole second, took third on a fly ball by Andre Dawson and scored on Brooks' hard grounder to third.

Steve Garvey's three-run homer helped San Diego take a 4-0 lead in the first inning.

*Phillies 6, Giants 2: In Philadelphia, Mike Schmidt's two-run homer broke an eighth-inning tie, lifting the Phillies over San Francisco.

With the score 2-2, Juan Samuel led off the eighth with a single. Schmidt then hit his eighth home run of the season on the first pitch from reliever Jeff Robinson (2-1).

Winner Steve Carlton (3-6) gave up two runs on seven hits in eight innings. Carlton, 41, set an NL record with the 666th start of his career, breaking the previous mark held by Warren Spahn.

" Carlton didn't throw many fastballs but he had a good slider and curve," said Giants Manager Roger Craig. "He doesn't throw as hard as he used to but he is a smart pitcher."

*Astros 5, Cardinals 4: Kevin Bass scored from second base on shortstop Ozzie Smith's throwing error in the ninth inning to give Houston the victory in St. Louis.

Bass opened the ninth with a single off Ken Dayley (0-3) and took second on a groundout. Mark Bailey was intentionally walked by reliever Todd Worrell, and Dickie Thon followed with a potential double-play grounder back to the mound. Worrell threw to Smith for a forceout, but Smith's throw to first base was wide.