It’s a painful red card to take and many referees would have settled for a yellow but it certainly isn’t a horrendous decision. Bear in mind he doesn’t have the protractor and compass like all the Jamie Carraghers on here to work out the speed of the other defender, the acceleration of forward and defender, the direction of the prevailing wind. It’s a foul and he’s probably the last man. Either card was only ever likely to satisfy 50% of the parties involved.