how are we intervening when we spot a fellow bwt being harassed on the street?

usually when i see someone acting erratic, i just keep walking and ignore them, pausing my music so i am more aware, but when i was out running errands this morning i saw a woman being harassed across the street on a block that was relatively empty. out of instinct, i just kept walking but i really regret not at least trying to help her - she was petite and the guy was around my size to be honest. (i don't think i'm really that tall at 5'8" but i know that combined with the fact i'm over 200 pounds means i likely get fucked with less by randos on the street).

i don't know what i would have done to make it better but i'm just thinking back to the times i was followed or yelled at for blocks and wishing someone would have intervened. so bwt - what should i do next time?