NCAA Question

[Odd Duck]

My sport is basketball, so I need some insight. I was attending a D3 game last week and noticed the officials rarely blew their whistle (even noticed it in the NFL but that may just be a sound issue). This game was physical and on several occassions a player down field but facing the line of scrimmage would get nailed by a player with his back to the line of scrimmage well after the action stopped...and it happened to players on both teams. There were never an flags and the game was well officiated.

My concern was that a player who knows the play is dead would relax and get hurt. Why no whistles?

Just curious.