Carlos in Green?

This move baffles me. When I heard that the Cs would be picking up the recently cut Carlos Arroyo, I didn't understand. I have not followed Arroyo's career too closely and the majority of my exposure to him was from this season when the Heat and Celtics played each other. In those games, Rondo made him look like a small child walking into the middle of the movie. He played as if he couldn't guard the 8-year-old Steph Curry from that NBA ghost commercial. (Although, that may be a bad example, young Steph was probably pretty wet.)

So I checked out his stats from this year: 5.6 points, 1.6 rebounds, and two assists per game. Not that sick. Then I examined his career numbers prior to this season: seven years, 7.2 points, 1.7 rebounds, and 3.3 assists per game. Slightly better, but again, underwhelming. And for a team that prides itself on defense, Arroyo, who couldn't check a Cheeto-stuffed Baron Davis, does not seem to be the answer at guard in Boston.

My best guess is they believe he'll be motivated after getting the shaft from the Heat to make room for our very own Mike Bibby (who, by the way, is averaging 2.3 points and shooting 14.3% from behind the arc in his first three games on the Heatles. Keep up the solid effort!) but that's the only reason I can think of. Anyone have a reasonable explanation for this? Or is Danny Ainge trigger-happy and/or bored since the trade deadline is over with?