Here we see quite an unusual photo. The Wrigley Field bleachers are full — including the portion that was blocked off in 1952 for a hitters’ background — but the center field scoreboard is unfinished, still under construction, apparently (you can see the right side incomplete).
The bleachers were built in 1937 — during the season. As I wrote here in 2013, construction sometimes continued during games, with one report that a construction worker was hit by a home-run ball.
Still incomplete, the bleachers opened to fans September 5, 1937, so this has to be after that, but before October 1, when the center field scoreboard was first put into full use.