There they were, seeking to amuse the packed rows of onlookers at the Macy’s Thanksgiving Day Parade on Thursday, ambling along amid the bobbing Hello Kitty and The Elf on the Shelf balloons, the preening majorettes, the blaring bands. They were simply a married couple blending innocuously into the merry procession, two of some 900 clowns more likely to be forgotten than remembered once it all ended.

They were clowns for a morning, nothing more. They wore matching outfits — snow-white suits decorated with blue trim and red stars, along with red-and-white striped sleeves and socks, white gloves and face paint.

The parade had barely begun. In its lengthy tangle, Robert and Irene Blasetti had reached the Avenue of the Americas and 39th Street. They were twisting balloon animals into shape for the outreaching children.

And then something happened that no one who witnessed it would forget.

Mr. Blasetti crumpled to the ground, flat on his back.