When one of these young men starts reaching into a bag, the other does not recognise the danger he is in, and does not react accordingly. Police pay special attention to this kind of behaviour because they may be reaching for a weapon.
Hard to imagine what these two were thinking would happen.
Complacent police surround man and fail to maintain a safe distance or keep their weapons ready. The man is able to close the distance and stab multiple police, possibly killing one before he is finally shot.