For some reason, Boston Celtics guard Marcus Smart has been on the receiving end of several in-game low blows over the course of his five-year NBA career.

It happened again on Monday night, when Dallas Mavericks guard Luka Doncic’s extended right leg accidentally reached Smart’s nether regions during the first quarter of their game at the TD Garden.

“I don't know what it is, I keep getting kicked in the groin. I don't know what it is,” Smart said post-game, per A. Sherrod Blakely of NBC Sports Boston.

Smart took the inadvertent hit like a champ and accepted Doncic’s apology shortly after.

The 25-year-old Oklahoma State product got the last laugh in the end, as the Celtics came away with a hard-fought 116-106 victory and stretched their NBA-best winning streak to eight games. The Cs also claimed solo lead for the best record in the league with an 8-1 slate.

Smart took on the hard task of trying to slow down the sensational Doncic for most of the game. The 20-year-old Slovenian still got his usual numbers of of 34 points, six boards and nine assists, but Smart made sure he worked for every bucket he had.

Smart pitched in 17 points and six assists in 37 minutes of action for coach Brad Stevens.

His frenzied approach on defense has earned him an NBA All Defensive Team First team last year. Standing at just 6-foot-3, Smart also remains as one of the most versatile defenders in the league, going up against faster guards and taller forwards on occasion.

Smart usually covers the opposing team’s best player, regardless of position.