Team Sky leader Froome, 33, a four-time Tour de France champion, fell away on the final climb of stage 17 and crossed the line in eight place, 48 seconds behind his teammate Geraint Thomas and one minute, 35 seconds behind stage winner Nairo Quintana.
The Kenyan-born Briton was cycling back to the Team Sky bus with a black rain jacket on, while some riders were still climbing towards the summit finish. Unfortunately, a police officer mistook him for a cycling fan that used to ride up the mountains stages to watch the race, and tackled him off the bike.
Photos on social media show a gendarme pulling Chris Froome by the arm, with his bike laying on the ground.
The incident came a day after police accidentally pepper-sprayed riders when trying to disperse protesting French farmers who blocked the road with bales of hay. The Tour de France was briefly halted after a large group of cyclers, including Froome, needed eye treatment due to the tear gas.
Five days before this year's Tour edition kicked off, cycling's governing body, the International Cycling Union, dropped an anti-doping investigation into Froome.
In 2017, he won the yellow jersey for the fourth time in five years.