Toward the end of an 11-on-11 scrimmage at training Monday, Carolina’s Kevin Jeffrey mistouched a ball out of bounds and gave up possession.

McColm Cephas ran to the touchline and scooped up the ball. Before throwing it back in play, Cephas told Jeffrey, “Too much concentration. [Expletive] off,” drawing hearty laughter from both.

Things are light in Carolina’s camp, but the RailHawks’ season is at its most crucial point.

The RailHawks (6-10-8) are in 10th place in USL-1 and trail Charleston by three points for the final playoff spot. With four games to play, they cannot afford another loss.

The RailHawks, 2-1-1 in their last four games, continue the season’s stretch run Sunday, when they welcome Montreal (11-4-8) to SAS Soccer Park at 6 p.m.

“If we lose one more game, our season’s over with,” said Carolina captain Frankie Sanfilippo. “Knowing it’s do or die, everyone’s fighting every game. We have that mentality that if we make the playoffs, we have a great chance to do well.”

Carolina is 0-2-1 against the Impact this season, and all three results were tough to digest.

In the first meeting, on June 8, the RailHawks squandered a 2-0 halftime lead and had to settle for a 2-2 draw. In the second match, on July 13, Carolina allowed a soft goal in the 84th minute and lost 1-0. In the third meeting, Carolina took a 4-1 thumping in Canada.

This weekend, however, will mark the first time the RailHawks will have their full complement of players available against Montreal, Carolina coach Scott Schweitzer said.

Perhaps the most important player back in the starting 11 is defender David Stokes. Stokes played Friday, when Carolina tied Atlanta 0-0, for the first time since July 20.

In the nine games Stokes has missed this season, the RailHawks are 2-6-1 and allowed nearly two goals per game. In the 15 games with Stokes in the lineup, the RailHawks have a 0.73 goals against average and six shutouts.

Stokes’ absence forced Sanfilippo to move from his favored right back position to central defense. With Stokes back and goalkeeper Chris McClellan (two straight shutouts) back to 100 percent, the defense that was so solid the first half of the season is once again intact.

“Everybody’s so used to that,” Sanfilippo said. “We do a lot of things on the right and we create a lot of stuff. It’s just a better fit. When Stokes is in, we have two big guys in the middle. It just opens up the field a lot more.”

If Carolina is going to make the playoffs, it will have to do something it has yet to this season: go unbeaten in four straight matches.

Carolina’s longest unbeaten streak this season is three games, but none featured what Carolina needs most — wins. In order to get three points from each of the next four games, Schweitzer said his side needs to continue doing what has allowed them to go 2-1-1 the last three weeks.

“We need to finish our chances for sure and continue to play defensively sound and not give up chances,” Schweitzer said.

In the last four games, Carolina has scored seven goals and allowed two.

If Carolina can go unbeaten the next two weeks, and if history is any indicator, they’ll make the playoffs. If they pick up 12 points in the final four games, they will finish the season with 38 points, which has been enough to put teams into the postseason the last two years.

The schedule could benefit Carolina, too.

They play Montreal and Portland, both of which have already clinched playoff berths, at home, and California and Minnesota on the road. California is already eliminated from the playoff picture, and the Thunder are dangerously close.

Montreal and Portland could rest key players, not wanting to risk injury or card suspensions, and California and Minnesota’s seasons may be over by the time the RailHawks visit them.

Carolina’s not banking on help from its opponents, though. The RailHawks know they need to do just one thing, regardless of the circumstance.

Said Stokes, “It’s the same it’s always been — we’ve just got to win.”