Lawrence Frank was happy. Lawrence Frank was angry. At the same time. The Pistons coach had just watched Jeff Green torch his club, scoring 11 straight Celtics points in the fourth quarter on the way to his 34, and while Frank couldn’t shake the feeling he’d just lost a very winnable game, he could manage what passes for a smile when your team has just lost its 51st game. Frank was a Celtics assistant when Green arrived from Oklahoma City in a widely panned trade for the popular Kendrick Perkins (a deal that isn’t looking all that bad right now). He saw him struggle in a number of different ways, and while Frank was gone to Detroit when Green had surgery to repair an aortic aneurysm and missed last season, he still has an affinity for the kid. “Jeff’s a very, very good player,” Frank said. “He got off to a tough start this year, and obviously he had major, major life threatening surgery last year. “He’s a high character guy, so you always like to see . . . I didn’t like to see him do well tonight, but by and large every other game you pull for him, especially with what he went through.” Putting aside the medical issue, which isn’t that easy to do, Frank was part of the staff that tried to get the most out of Green as he adapted to the Celts on the fly in the last few months of the 2010-11 season. “The thing with him was coming in in the middle of the year with a veteran team that’s so ingrained in terms of doing what you do, it’s a tough spot,” Frank said. “And remember, Jeff’s a young player. Most of his minutes were as a backup 3 (small forward), which, if you remember at Oklahoma City, he was playing more of a range-shooting 4 (power forward). He’d start at 3, but at the end of the day they played him at 4 with (Serge) Ibaka or (Nick) Collison at 5 (center). “That’s what’s most impressive to me, how comfortable he is playing the perimeter spot like he is. Doc (Rivers) was doing a lot of posting him that year. Now you see his perimeter game. He’s shooting the ball well — one or two dribbles, ability to get to the rack. And I just think the confidence; he has a whole different presence about him, just a very confident thing.”