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[NoFussRef]

I would go intentional foul on this.

I can't see calling it flagrant, but what I see are the arms/hands purposefully extended into the rebounder. If he hadn't extended into the rebounder I could see just a run-of-the-mill personal foul.

As for flagrant, my job is not to read the mind of the fouler, just view the action and rule on what I saw. Makes no difference to me if the player fouled is their star, or their weakest bench-warmer.