4 - the number of WWE Hall of Famers in the first Women's Royal Rumble Match

When excluded the champions and injured WWE Superstars, there were only 18 announced entrants for the Royal Rumble match. That left a lot of room for several surprise returns, and of those surprises, four of them were WWE Hall Of Famers.
Lita entered the Royal Rumble at #5 and was inducted into the WWE Hall Of Fame in 2014. Jacqueline entered the match at #21 and was inducted into the HOF in 2016. Beth Phoenix entered the match at #24 and was inducted into the HOF just last year in 2017. Finally, Trish Stratus entered the match at #30 and was inducted into the HOF in 2013.
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Of these four women, Lita lasted the longest in the match at 5:51, but Trish had the most eliminations with three.