Long story short, lots of child actors and metal, sharp weapons swung haphazardly at them by unskilled extras. Luckily nobody was injured and it was brought to someone's attention that mayyyyybe thats not a good idea.
http://deadline.com/2015/07/divergent-series-allegiant-child-actors-risk-whistleblower-1201475599/
"Thirty child actors – some as young as 4 years old – were put at risk during the filming of a battle scene last month on the Georgia set of Lionsgate’s Allegiant. In the chaotic scene during production of the third film in the Divergentseries, child actors scrambled through a gauntlet of more than 100 untrained adult extras swinging metal clubs, axes and machetes."
“Concerned, I went around and handled the weapons for myself and saw that they were steel and aluminum, with bladed edges, and some were quite sharp.”
http://deadline.com/2015/07/divergent-series-allegiant-child-actors-risk-whistleblower-1201475599/