It’s a baseball diamond.

For non-unitedstatesians: typically, on a purpose-built field, the backstop (behind home plate, towards which the pitcher throws the ball (pro league can reach ~100mph/160kph) and the dugouts (where the teams sit) are shielded in some fashion. Here, they’re using chain link.

Right‽ Both of us here maintaining the fields just stopped and watched it for a couple minutes. It was mesmerizing