I've always thought that it should be given as obstruction, since that would be the decision elsewhere on the field. However, shirt pulling and what amounts to assault when waiting for a corner to be taken seem to be acceptable to most referees in the modern game, but a fair attempt at a tackle that is mistimed by a fraction of a second will bring a yellow card. Ninety percent of referees now give a foul for a true shoulder charge. Times have changed and the rule book needs to be either rewritten or reread.
I remember that when playing schoolboy football in the fifties, a referee (teacher) would give a foul for raising the forearms above waist height, and if you argued would want to know to what purpose you were doing it. One teacher would suggest that if you were so keen to raise your arms, boxing lessons could be arranged after school.
The change to the game started to creep in when Spurs were playing European games in the early sixties and we would shout at the tele at referees allowing the "continental" foul.
