With the traffic inside it may very well be more difficult to detect.
Ekuban, #50, late in the game was mauled coming around the left side, the offenses right, so bad he was bent backwards....no call. A couple plays later the SEattle right tackle gets callled for holding....it was without a doubt the sorriest holding call I remember. He barely grazed the defenders facemask...not grabbing it or pulling it, just sliding his hand across it.
You maybe right that the officials are not in a good position and there is too much clutter inside....I have no answer.
