Celebrating directly towards opposition supporters is treated far more seriously than any other form of celebration. The reason lies in what happens in the stand rather than on the pitch.
The offence is about the crowd, not the opponent
Provoking players is handled through the ordinary disciplinary framework and usually amounts to a caution at most.
Provoking a stand is different, because the response comes from thousands of people who are packed together and cannot be individually managed.
Objects thrown, surges towards the front rows and confrontations between rival sections all follow from moments that begin as a gesture.
Stewarding is built around predictable flashpoints
Safety planning identifies the moments most likely to produce disorder, and a goal celebrated in front of the wrong section is high on every list.
Stewards position themselves at segregation lines before set pieces and corners precisely because those are the moments a scorer ends up near away support.
A celebration that pulls players towards that line disrupts the plan at the exact instant the crowd is at its most volatile.
Clubs carry the consequences, not just players
Disciplinary systems hold clubs responsible for crowd behaviour, so disorder following a celebration can produce sanctions against the club itself.
That creates a direct institutional interest in preventing the gesture, which is why managers address it publicly and privately.
The player receives a caution, while the club may face a fine or a partial closure, and the imbalance shapes how firmly it is policed internally.
Derby matches concentrate the problem
Local fixtures combine larger away followings, tighter segregation and existing hostility, so the same gesture carries more risk than it would elsewhere.
Players from the area understand the significance better than anyone, which is exactly why the temptation is strongest for them.
Clubs frequently brief squads before these matches, and the briefing is about crowd safety rather than about respect for opponents.
Where the line actually sits
Celebrating near away fans is not itself an offence. Running deliberately towards them, gesturing, or inviting a response is.
Referees judge direction and intent, which makes this one of the more subjective calls in the disciplinary code.
The inconsistency people notice comes from that subjectivity, and removing it would mean banning celebrations in whole areas of the pitch, which nobody has been willing to do.