I have been out of competitive sports for a decade or too, I have clue what that black thing is that resembles a sports bra. The image was taken at the win Europa Conference League final, won by Olympiakos vs Fiorentina.
I've been watching the reality show Welcome to Wrexham about the real Wrexham soccer team that 2 American show business guys own. I've noticed most of the soccer players wear this. (Lots of locker room shots in the show.) As far as what it is...
“They might look like sports bras, but in fact they’re athletic vests designed to hold GPS trackers. Those vests need to be skintight so the pod that actually acquires the data – which is slipped into the back of the vest – can monitor players’ performance.” "Why are the players wearing sports bras?!" | An answer to the burning question | New England Revolution
Our players wear them too. It’s a fitness tracker and keeps a log of a myriad of stats. Why do Football Players wear GPS vests? - Catapult One