Borussia Moenchengladbach striker Marcus Thuram faces a lengthy ban after he was sent off for spitting in an opponent's face.
With the scores locked at 1-1 in the 77th minute, Thuram went to ground after a challenge from Posch.
Thuram then spat from close range at Posch, who reeled back wiping his face.
Thuram walked away with Posch in pursuit as the game continued before the referee Frank Willenborg consulted with the video assistant referee.
Thuram was issued a red card and Posch a yellow, for his part in the incident, before he was substituted.
"It's a shame for the team and a shame for him," Gladbach teammate Valentino Lazaro said.
"It doesn't fit with his character at all."
Midfielder Christoph Kramer was less understanding, saying: "His fuses blew. You can't excuse it."
Gladbach coach Marco Rose apologised "on behalf of the whole club".
"It simply doesn't belong on a football pitch. It goes way beyond the limits," he said.
France international Thuram - the son of Les Bleus World Cup winning defender Lilian Thuram -could face a suspension longer than the five games served by Schalke defender Ozan Kabak after he spat in an opponent's direction in September, but missed.
Posch's replacement Kevin Akpoguma laid on the winning goal for Ryan Sessegnon four minutes from time as Hoffenheim grabbed a 2-1 victory.