I have seen old videos of fans running onto the parquet in the Garden after the Celtics won the championship. Is this still done? If not, when did this stop being allowed?
Whether or not it is "acceptable" isn't the real question in this scenario because you can't do it in the first place. Acceptable to whom? It may be acceptable to other fans and even players, but there is too heavy of a police/security presence to be possible. See Masai Ujiri's incident at the recent finals. The team's president wasn't allowed on the court, with credentials, after the Raptors won.