WALTHAM, Mass. -- Boston Celtics strength coach Bryan Doo huddled the team's players at midcourt at the start of Tuesday's practice and, with what looked like a miniature foam basketball in one hand, quickly explained the rules to a warm-up game that, essentially, proved to be the playground staple keep-away.

But this wasn't child's play. And maybe underscoring just how competitive the Celtics have been in training camp, the team's 18 available players clumsily launched into a match that rapidly escalated in aggression. White jerseys began swarming ball handlers in green, who quickly lateraled across the 50-foot court while looking to avoid the oncoming rush and advance the ball.

It lasted only a few minutes before Dad, err coach Brad Stevens, blew his whistle and the team scattered into more standard 3-point shooting drills to start an afternoon session. Hey, it's not as if the team needs a whole lot of work on ball movement at the moment.

No, if there's one area where the Celtics have excelled since the start of training camp, it's moving the basketball. That much was obvious as early as the team's intrasquad scrimmage in front of season-ticket holders in the first days of camp. The ball zipped all over the court that night with both sides generating easy looks while rarely letting the ball stick.

That continued overseas where Boston averaged 117.5 points in two exhibitions, generating assists on 65.5 percent of its total field goals. Even in a very small sample against non-NBA competition, that's an encouraging number. The Celtics tied for third in the NBA in assist percentage last season at 62.9. The only two teams better? The Eastern Conference-leading Hawks (67.6) and Western Conference-leading Golden State Warriors (65.9).

And it shouldn't come as a surprise that Boston's assist percentage went up a tick in the second half of the season. After being at 62.5 percent over the team's first 46 games, Boston jumped to 63.4 percent as part of its 24-12 stretch in the final 36 while surging to the seventh seed in the East.

Quantifying good ball movement is no easy task and assist percentage is a pretty rudimentary metric (heck, the 76ers were eighth in the NBA at 60.9 percent and it didn't exactly help their cause). Even with more advanced numbers delivered by camera tracking, there's not always magic in, say, the total amount of passes. A crisp two-pass push up the floor for an easy layup is just as valuable as cracking a defense with a bevy of quick passes in a half-court set.

Ball movement is more of an eye test, and the Celtics are pleased with what they see so far.

"Especially at the beginning of preseason, the teams I've been on it's like, 'Man, we've got to move the ball a lot better,' " point guard Isaiah Thomas said. "This team, that hasn't even been a question. Coach has kind of been like, 'You guys sometimes pass a little too much. You guys are passing up some really good shots to try to be a little too unselfish.' I guess that's a good problem to have. That's probably what stood out to me when I watched film, how good we move the ball. We haven't even been together that long and it's only been a couple weeks of training camp so that's a good sign."

Ball movement has always been a priority for Stevens. He's gushed about the way the San Antonio Spurs zip the ball around the court. Few things tend to get Stevens as excited as when quality movement leads to an open bucket.

An example: The Celtics were on their way to a comfortable win over the Indiana Pacers in early April last season. With around two minutes to play in the fourth quarter, Boston appeared to get bogged down in a half-court set but some quick passes, a couple of screens, and an Evan Turner drive caused enough shuffling that Turner was able to find a wide-open Avery Bradley beyond the 3-point arc. Stevens, the same guy who barely blinks when the team completes a last-second game-winner, clapped his hands and sprung from his chair as Bradley received the ball (and applauded his players again after Bradley made the triple).

Stevens has often repeated, "We're best when the ball moves."

Boston's best isolation player, Thomas, can create on his own, but Stevens has singled out his performance as a playmaker during camp. The Celtics are seeing the benefits of simple, unselfish play.

"Guys are just playing for each other," Thomas said. "I always say that. I think guys are trying to make the game easier for each other and that's the motto of this team -- just, if you don't have a play that you can make for yourself, make one for another guy."

Marcus Smart, the team's projected starting point guard, said Boston has put an emphasis on two areas: playing hard and playing unselfish.

"Our effort was unbelievable [overseas]. We were playing hard," Smart said. "We definitely have a lot of things to work on, but for the most part we played very well. Everyone was very unselfish with the ball and just unselfish as a team, so that was a good thing. The other things will come to us."