Origins
Behind the violence of assault lies a surprisingly athletic image. The word descends from Latin assilīre — 'to leap upon' — composed of ad- ('towards') and salīre ('to leap'). An assault was, at its core, a physical pounce.
Latin salīre meaning 'to leap' is one of the most fertile roots in the language. A salmon is etymologically the leaping fish, named by the Romans who watched it vault up waterfalls. Salient means 'leaping out' — a salient point is one that jumps at you. A result leaps back (re- + saltus). An insult originally meant to leap on someone. Exult meant to leap for joy.
The word entered English through Old French asaut in the 13th century, spelled without the 'l'. Renaissance scholars later re-inserted the letter to honour the Latin ancestor, giving us the modern spelling assault with its silent consonant.
Latin Roots
In law, assault and battery are technically distinct. Assault is the threat — the leap begun. Battery is the contact — the landing. This distinction preserves something of the original Latin image: the moment of launching oneself at a target, before impact.
The most playful descendant may be somersault, from Old French sombresault, from Latin supra ('over') + saltus ('leap'). A child turning a somersault and a soldier mounting an assault share the same ancient word for jumping.