That he contravenes a law is not in doubt. You cannot leave the field of play without the officials permission.
The issue is that dozens ofothers do it without a card.
Dean had the 'duty' to book Sterling, only if he is following the absolute letter of the law & decides, himself, that Sterling approaching the fans raised a security issue.
As opposed to Wayne Rooney clearly 'gesturing or acting in a provocative, derisory or inflammatory way' in front of me, last Monday.
If you read the second bit, Dean also had 'no choice' but to book the Bounemouth players for time wasting, yet strangely enough, seemed to 'choose' not to.
CELEBRATION OF A GOAL
Players can celebrate when a goal is scored, but the celebration must not be excessive; choreographed celebrations are not encouraged and must not cause excessive time-wasting.
Leaving the field of play to celebrate a goal is not a cautionable offence but players should return as soon as possible.
A player must be cautioned for:
- climbing onto a perimeter fence and/or approaching the spectators in a manner which can cause safety and/or security issues
- gesturing or acting in a provocative, derisory or inflammatory way
- covering the head or face with a mask or other similar item
- removing the shirt or covering the head with the shirt
DELAYING THE RESTART OF PLAY
Referees must caution players who delay the restart of play by:
- appearing to take a throw-in but suddenly leaving it to a team-mate to take
- delaying leaving the field of play when being substituted
- excessively delaying a restart
- kicking or carrying the ball away, or provoking a confrontation by deliberately touching the ball after the referee has stopped play
- taking a free kick from the wrong position to force a retake