Rule reminder
A key difference from English: Italian perception verbs (vedere, sentire, ascoltare, guardare, osservare, notare) NEVER take the gerund (-ando/-endo). Where English says 'I saw him running', Italian says 'L'ho visto correre' (bare infinitive). This is one of the most common errors made by English speakers.
I saw him running down the street. → L'ho visto _____.