I've seen this lyric issue debated on the Internet quite a bit. My personal view is that people are reading too much into it. I believe the official lyrics "high hopes hailla ball" were likely the words Robert originally wrote for the song, and intended to sing, but when it came time to sing them for the recording, which according to Led Zeppelin lore and the spoken lines in the beginning of the song from John Bonham indicate was the fifth take, he simply 'muffed' the words and it came out sounding like what most people hear: "hell high hailla ball". I'm a singer in a band and that happens all the time. Since the rest of the vocals of that particular 'take' were otherwise good, they probably just let it go as it was - not letting ‘perfect be the enemy of good’. When it came time for the lyrics to be published with the album, however, the record company guy responsible for that probably ended up getting Robert's original 'intended' lyrics - not what he actually enunciated on the recording. BTW: In guitar tab books for the song the line is usually written as "high hopes hail-a ball". In addition, I actually hear "held-high haillas ball" on the original recording, which aside from the ‘s’ in hailla, I think makes a bit more sense for the song context, if this pronunciation was actually intended, than ‘hell high’ or ‘hellhound’ (Robert Johnson reference) as some suggest. Just an opinion.