It's quite serious. Although a misdemeanor, this type of charge can lead to long term no-contact orders, orders prohibiting access to the family home, firearms prohibition, jail, and massive fines. It carries a maximum potential of a year in jail, and a $5,000 fine.
It obviously looks horrible on a criminal history, and can derail school and employment opportunities. Your friend does need to take this very seriously, talk to a lawyer right away and follow his advice.
If the defendant is not a US citizen, a conviction of or guilty plea to domestic violence against certain household members likely will lead to the deportation of the convict.
If the defendant is not a US citizen, the defendant should thoroughly review the immigration aspects of the case with his attorney.