Andrew Bynum's forearm hit on Jose Juan Barea was a cheapshot, and completely deserving of an ejection, fine, and probable suspension.
The Lakers' center is a skilled big man and not a thug bruiser in the mold of The Bad Boys, a Detroit Pistons team in the late 1980s that was known for delivering hard fouls.
The foul on Barea certainly seemed like something Bill Laimbeer or Rick Mahorn would do, but for Bynum, it was a little out of character. With the exception of an earlier hard foul on Michael Beasley in the regular season, Bynum has not been known for such hostility. He has avoided fights, and has been cautious of getting into foul trouble, which plagued him in the early part of his career.
So why did Bynum do it?
There's no excuse for such action, but the foul wasn't completely unwarranted or surprising.
First, Barea gave an overt push off on Steve Blake as he drove the lane, and no foul was called, which prompted Bynum to retaliate. Such retaliation is typical in teams sport, not just basketball. If a player gets hit, it's up to his teammates to have his back.
Second, small guards penetrating have often been met with a harsh foul. Centers take it as a personal insult if they are challenged. Bynum could have gone for a block instead of a forearm, but with the score out of reach, he decided to send a message instead. Back in the 1960s, it was an unwritten rule that small guards would pay a price if they drove on big men.
Three, Bynum was probably exhausted and demoralized. The Lakers looked tired, and Bynum probably wanted to be ejected so that he can get off the floor, when a comeback was basically ruled out. It was painful to see Barea continue to torch the Lakers, so Bynum took action.
Four, Bynum acted on frustration. The Lakers were expected to go deep into the playoffs and getting swept by the Mavericks was not what many expected, particularly the Lakers. With the game out of reach, Bynum acted on the frustration of a season coming to an earlier-than-expected conclusion.
Five, Barea shouldn't have been driving to the hoop with the Mavericks up by 33 points. When a team has a big lead, it's customary to take your foot off the gas pedal. By Barea attacking the hoop, it comes off as a pouring it on. Barea should have anticipated an unpleasant reaction from the Lakers.
Six, Bynum is still a little immature. It's easy to forget that he is still only 23. He's been in the NBA since he was 17, but he's still young and makes errors in judgement that many young players make.
Bynum's foul was a mistake. It will be up to him to move on, and make strides in this off season.