Ken Singleton, 1981 Kellogg's #39

I wish that Kellogg's had put cards like these in their cereal boxes during my childhood. The ethereal blur of the background image really makes the player's portrait pop. It's more visually interesting to me than the lenticular "moving" images that Kellogg's used on the cards that were inserted into cereal boxes when I was a kid. There were also 66 cards in the 1981 set, as opposed to the scant 15 released in 1991. Of course, there's something puzzling me about Ken Singleton's card. I have no idea what is floating in the background over Ken's right shoulder. Is it the top of a batting cage? A construction crane? A skywalk to nowhere? Your thoughts?