I am of the opinion it was a dirty play but that the intended effect wasn't to be so malicious. It's gamesmanship. If you watch the whole play, Webster has his left ankle around Tim's right calf in mid-air. Tim whips his right leg free and turns his body to the left 180 degrees to face upcourt. Webster goes down hands first, he could have chosen to go chest after but he decided to roll.
The opportunity is to take Duncan out of the play, not to injure him. If Tim just falls on top of Webster with no injury, then it's a 4 on 4 instead of a 5 on 4 break. He rolled towards Tim in an effort to take him out of the play. Not to take him out for the season or worse. He seemed genuinely concerned so kudos to Webster for that, but that play, to me...seemed unnecessary.
Just thank the man above that the brace is all about protecting Tim. Punisher was on the job.