Yes, the whistle was delayed. I dont really care if its right. It could have been a no call except for the fact that Simmons pinned Mitchells arm forcing the ref to make a call. Which is a smart move by Simmons. If the ref is forced to make a call he is going to call the first foul which is Mitchell. I uploaded the last 2 minute report into my video analysis software I use for work, unfortunately the quality isnt great. But here is the picture of the first contact. It clearly shows Simmons arm up in the air and Mitchells arm reaches all the way around Simmons.
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I will also the video of it.. It is the first contact and by the NBA definition a hook. It was a bad play from Mitchell among many at the end of this game. I think Mitchell is great at the end of games in his career though and he will figure it out. He will be clutch in the finals this year.