Is it stocking up or worse? Please help.?

Something similar happened to my mare a few weeks ago, except hers was caused by a small cut on her leg, it swelled because of infection, it wasent hot and the swelling itself didn't hurt to touch it but the cut was really sore, I would call a vet and get it checked out, it may be a pulled ligament, which may be serious or it could be something really simple, regardless I would get it checked out,, there's no cut or abreason to explainthe swelling, better safe than sorry :)