I know the Assignor for this league. He said that the umpires did the right thing in clearing the field immediately when they saw that lightning was in the area. Unfortunately for one woman who chose to remain, she was injured by a nearby strike.
The lesson here for umpires is to clear the field at the first sign of a lightning strike. Don't wait. It isn't worth it.
ER nurse in right place at right time when woman is injured by lightning strike
http://www.9news.com/weather/er-nurse-is-in-the-right-place-at-the-right-time-when-woman-is-injured-by-lightning-strike/437640311