I saw an episode the other day where Buffy had crutches but they didn't seem to address it. Did I miss something? Did she hurt herself in real life?

Yes, before the filming of season 4, Anissa broke her leg and it was incorporated into the storyline--she was in a cast almost the whole season for 2 reasons--one, the rapid pace they had film scenes to fit Brian Keith's contract (he worked only 2 months out of the whole year for the show) and the fact that Anissa re-broke her leg while it was healing, causing it to be further in the cast.

It is amazing how Brian was on the set for 2 months filming ? 30 some odd shows that would run for the next 9 months

It is amazing how Brian was on the set for 2 months filming ? 30 some odd shows that would run for the next 9 months
Fred MacMurray did the same thing on My Three Sons. (for 12 seasons!!!)

Anissa broke her leg while surfing.