Lindsay Lohan's father Michael was assaulted

The night before Lindsay Lohan needed to attend Beverly Hills courtroom, her estranged father, Michael Lohan, was assaulted in Santa Monica according to authorities.

According to police, he was getting into his car, then a man approached him and there was a fight. Then the attacker fell down and then he ran off after that.

No arrest done yet.

I wonder why that person attack him?

Source