According to The Mirror, Ronson became enraged when she spotted Lohan dancing with her ex Best at London's Boujis club.
A source said: "Sam had had a few cocktails earlier in the evening and was perhaps a little more emotional than usual. While she was in the VIP section, Calum shimmied up to Lindsay on the dancefloor. Lindsay was lapping up the attention, having a laugh - and a flirt. But Sam saw them and went ballistic.
"She marched over and started pushing and shoving the pair, demanding to know what the hell they were playing at."
As the fight escalated, Ronson and Lohan allegedly began "swearing and screaming like banshees" and were pulled apart by Best.