There's been a bunch of times where it should have been enforced. A few years ago the 49ers purposely, simultaneously, held both receivers and accepted the five yard holding penalty. Only a few seconds 'til halftime, Saints were forced to kick a FG.

One egregious example was Tomlin wandering out onto the field during a kick return. Returner had to dodge him and was eventually tackled. Should have been ruled a touchdown, was not and Ravens settled for a FG.

HERE WE GO BROWNIES! HERE WE GO!!