The incident occurred as the debate over childcare was coming to an end.
The Deputy Speaker told meeting members to “take it easy” before moving on to the next item.
However, Nicholl stood up and asked for a point of order, to which the Deputy Chairman replied: “Go ahead”.
Points of order are a mechanism through which members of the assembly can raise an issue relating to the rules of parliamentary procedure.
Nicholl asked whether “it is correct that the Education Secretary is implying that Alliance ministers did not support the £25 million for childcare”.
While Nicholl was speaking, Lyons stood up and walked out of the room, which took him past where Nicholl was standing.
Because he didn’t have a microphone, it’s not possible to hear anything he said on the meeting’s live feed on his way out.
However, after he left, SDLP member Sinéad McLaughlin said Lyons “screamed at Nicholl ‘sit down’”.
Nicholl posted on social media after the incident that Lyons’ comments were “aggressive and arrogant and I have to say, I doubt this would have happened if I was a man.”