BOSTON — Former Boston Celtics captain Rajon Rondo acknowledged Friday that he “hasn’t played defense in a couple years,” and suggested that the recent trade that delivered him to the Dallas Mavericks has reinvigorated him, particularly on the defensive end.

While addressing his return to Boston after Friday’s shootaround at TD Garden, Rondo said what a lot of Celtics observers have long speculated: That his effort on the defensive end had waned, especially when the team dropped from contender status in recent seasons.

“I haven’t played defense in a couple years,” Rondo said. “I’ve been able to hide a lot with Avery Bradley on the ball. He’s helped out, the young guy. But [in Dallas] they expect me to play defense and, in the West, if you don’t play defense you’ll get embarrassed every night at the point guard position.”

Celtics coach Brad Stevens smiled when apprised of Rondo’s comments, but declined to offer a response.

“I don’t know the context of the discussion. I don’t know the seriousness of his answer,” he said. “I don’t really have any reaction to that. He’s a really good player, and I’m certainly not here right now to be critical or analytical of his comments to the media. I think, like everybody else, I’m excited for him that he’s in a great opportunity and has a great opportunity in Dallas. I hope that we play well against him tonight.”

The Mavericks are 5-2 since Rondo’s arrival, including Friday night’s 119-101 win against his old team. Rondo starred, scoring 29 points to go with six rebounds and five assists.

Entering Friday, the Mavs’ defensive rating with Rondo aboard has improved by 4½ points while dipping from 105.1 points per 100 possessions over the first 28 games of the season to 100.6 in the six games since his arrival.

Rondo’s individual defensive numbers haven’t changed much, according to the league’s player tracking data. Entering Friday, his opponents shot 50.3 percent against him in 22 games with Boston this season (5.1 percent above those players’ season averages), and that number is up slightly to 51.6 percent (and 5.8 percent above those players’ season averages) over six games with Dallas.

But the eye test suggests a far more inspired Rondo on the defensive end, particularly while going against some of the top guards in the West.

“I took it as a challenge in myself and it’s not just me, it’s my teammates,” Rondo said. “Our communication is getting a lot better and our coverages are getting better. It’s the whole team concept. It’s not just me. People want to look at the stats and say, ‘Since Rondo came there they have been down 7 or 8 points’ or whatever it is defensively. We still have a lot of room to improve and I believe we’ll still get better defensively.”

For the 22 games that Rondo was with the team this season, the Celtics owned a defensive rating of 103.2, ranking 16th in the league through the trade on Dec. 18. Since that point entering Friday, Boston owns a defensive rating of 99.1 over the past six games, which ranks sixth overall in the league in that span.

Boston’s defense had improved in December even before the Rondo trade, but the numbers are even more glossy since his departure.