Biting leash only after play...Help!

[daveyboy]

I have a 7month old female border collie. When i take her for a walk and JUST a walk it goes well. Shes at the point where she walks well enough, meaning, she still sometimes pulls and tries to lead but thats about it. Walking on leash has improved but still more area to improve. I take her to this large public park everyday to play frisbee. Shes getting REALLY GOOD! I have her on a 30ft lead just because i dont completely trust her in a public park yet with people, children, and other dogs. She does very well on the long leash and if she gets to nosy and starts to wander i can stop and let her know thats, "too far" and,  "comeback". 90% of the time the frisbee is more fun and entertaining then everything else. The PROBLEM comes in when its time to leave. I wrap up the long lead and switch her over to her shorter leash for the walk home (real close, 1min30sec walking). She goes nuts, biting and jumping at the leash, things she doesn't do when we just go for a walk. I try to use commands we've taught like "leave it!" and tell her to "walk". She'll abide but only momentarily. Sometimes i can get her to stop jumping and biting at the leash but she runs furiously to and fro up and down while on the leash the whole way home. Not sure if i should just be patient and chalk this up to her being amped up from play and being a puppy, or its her just not wanting to stop play so she throws a tantrum. Is it something im doing that I could change? It just makes this wonderful and enjoyable experience we have end in frustration in the short walk home. Please lend me any advice and wisdom, thank you!