For Carroll it has always been about winning, a subject he knows plenty about.
He has been a starter for two teams that won the MLS Cup, - D.C. United in 2004 and the Columbus Crew in 2008.
Last season, when the Union didn't make the playoffs, it was the first time since he became a starter in 2004 that Carroll sat out the postseason.
Now in his third season with the Union, Carroll is a defensive midfielder who does a lot of the grunt work that outsiders certainly don't appreciate as much as his coaches and teammates.
"We call him the Iron Man," said 22-year-old defender Amobi Okugo. "The amount of running he does, it is amazing he has lasted this long in the league and it's a credit to him and his ability."
Okugo then described the essence of such a selfless player.
"He is one of the more underrated players in the league but he doesn't really care," Okugo said.
Team manager John Hackworth took it a step further. "Brian is a guy our coaching staff leans on a lot," he said. "He is the player, day in and day out, that is our leader."
It's no surprise that Carroll is the team captain. Yet unlike many captains, he isn't one who provides too many words of inspiration. What makes him such a great leader is that he doesn't have to say much to get the team to follow his lead.
"His actions are huge and there isn't a harder working individual in the locker room or the field," Hackworth said.
When asked if he sees any irony in game No. 300 coming in the place he started his career, Carroll briefly got reflective.
"I do, a little bit," he said. "It will be extra special to have my family here to kind of enjoy the milestone."
What has motivated Carroll so long is what will be driving him on Saturday - the chance to get closer to clinching a postseason berth. The Union have 45 points and are in the fifth and final Eastern Conference playoff spot, two points ahead of No. 6 Chicago with three games remaining.
When asked what it would mean to return to the postseason after last year's absence, Carroll didn't hesitate.
"It would mean everything."