Here's some reasons where it would be considered a federal crime.
'Today, there are plenty of federal aspects to domestic violence that people need to be aware of if they are charged with any form of domestic violence. For example:
Additional charges may be brought by the Bureau of Alcohol, Tobacco, and Firearms (ATF) if you brandished a weapon during a domestic altercation.
Domestic or intimate partner violence that occurs when someone crosses onto Native American reservation lands is prosecuted as a federal crime.
Under VAWA (Violence against Women Act) your case will fall under federal jurisdiction if you cross state lines and stalk, harass, intimidate, or harm a domestic or intimate partner.
The Gun Control Act makes it a crime to possess a firearm or ammunition if you are currently subject to a restraining or protective order.'
https://www.schlosserandpritchettlaw.com/domestic-violence-can-federal-crime/