Assault on a Federal Officer

Assault on a Federal Officer - whoever forcibly assaults, resists, opposes, impedes, intimidates, or interferes with any person designated as an officer or employee of the U.S. while engaged in or on account of the performance of official duties; or forcibly assaults or intimidates any person who formerly served as an officer or employee of the U.S. on account of the performance of official duties during such person's term of service shall be guilty of the offense. If the acts amount only to simple assault, then she/he may be fined or imprisoned not more than one year, or both. Where such acts involve physical contact with the victim of that assault or when there is intent to commit another felony, she/he shall be fined or imprisoned not more than 8 years, or both.
If a deadly or dangerous weapon (including a weapon intended to cause death or danger but that fails to do so by reason of a defective component) is used to commit the offense or when there is infliction of bodily injury the penalty is more. The offender shall be fined or imprisoned not more than 20 years, or both.

Source: http://definitions.uslegal.com/a/assaulting-a-federal-officer/