When it's a footprint made on a putting surface that's covered with frost. It's hard to believe that simply walking across a golf green covered with frost can cause so much damage, but the proof will be there in a few days as the turfgrass dies and leaves a trail of brown footprints. That's why most courses will delay starting times until the frost has melted. And it's also why golfers who appreciate a quality putting surface will be patient during frost delays.
Greens are fragile.
The putting surface, or green, is an extremely fragile environment that must be managed carefully and professionally. Remember that every green is a collection of millions of individual grass plants, each of which is a delicate living thing. Frost is essentially frozen dew. The ice crystals that form on the outside of the plant can also harden or even freeze the cell structure of the plant. When frosted, the normally resilient plant cells become brittle and are easily crushed.