you mean warm up, not stretch, right ?

Stretching happens after if ever, not before :)

The philosophy of stretching changes every couple of years. One year, stretching before is the way to go. Then, stretching after sport. Then, no stretching at all.

From what I know: Stretching after doing a workout is bad, because it tenses muscles even more, stopping the flow of blood in the muscle and thus, making muscles more sore. But maybe that opinion is just the current trend.

The science on this one seems clear, stretching is only useful for increasing range of motion. It doesn't prevent injury ( in the studied contexts), it doesn't prevent DOMS, and it doesn't lengthen muscles.

on phone, but sources are a quick search away.

The solid science has been pretty consistent for about 20 years: dynamic stretching can be helpful, static stretching much less so, and the best warm-up for an activity is doing the activity at a lower rate for a few minutes.