What is this?
It would be helpful to know where in the world you are located
I am in Ontario, Canada, near Fenelon Falls. Gardening zone 4b. This is north of Toronto, Ontario, Canada, and 1 zone colour than Toronto.
I think it might be crown vetch, but hard to tell with picture of just the leaf. It is a legume that invades prairies and low-maintenance turf. Prior to being found to be invasive it was planted on highway medians too steep to mow.