Not sure if you read the thread about candids at this forum. It was in winter.
Good read to learn about candids. So, it is not my technique.
Also seconds for selecting of AF on shallow aperture will kill the moment more likely, compare to AF on wide lens without USM.
If I want candids with big aperture, I'll use camera with big VF and AF switch turned to off and I'm not the young one as well.
Candids are candids at day or night. I'm not into late night shooting. But with cameras I have ISO1600 or higher works well for 5.6 in low light.
This guy was running way ahead of me. I prefocused at 28mm and f5.6 at something near by me and once he was at the distance I want him to be I pressed shutter release to get another one on the board as well.
To get candid picture like this I wasn't even looking to VF, I was holding camera just like I'm not shooting at all.