Fair Use us quite vague, but basically a short clip would to the trick...I think the point of Fair Use is intentionally left that way, but when used in moderation, it's does its job. The problem is, I doubt Google hand-selects each video for individual inspection unless flagged for removal; they probably just search for key words in titles, tags, and comments...and wipe them out indiscriminately.
My personal opinion, regardless of law, is that any work that is not later available for sale, should be permitted for simple redistribution after a period of one year. It's not as if it will ever be re-broadcasted again, after that time, and would not be of any detrimental loss to the originator. Examples would be old news broadcasts, sporting events, live programming. The catch would be that they cannot be sold for profit after that point, and that no derivatives can be from it, without expressly written consent, so on...
My point is while many TV shows and scheduled programming are sold in box sets after a year or so, or shown again in syndication, there are many programs that are never transmitted again, for they have a limited value to sponsors and a limited audience once aged...much of it just winds up in a storage room, anyhow. [/opinion]
Anyhow, the law is the law. Check back in 100-120 years or so, when it becomes part of public domain.