During a fight, some fighters extend their arms defensively to keep distance between them and their opponents or in order to use trapping tactics to attack with elbows.
The worst thing fighters can do to counter this is to do what Rashad Evans did against Jon Jones, which is to extend their arms to touch their opponent's hands.
To counter this arm reaching/extension, the best way for fighters is to make their opponents pay every-time they extend their arms by low kicking or attacking them in the body.
Here is Rashad landing a low kick. Notice Jon’s arms dropping:
In the sequence below, Rashad Evans kicks Jon Jones forcing him to retract his extending arms:
My original post: https://www.bloodyelbow.com/2017/7/20/15956234/defeating-the-goat-how-to-beat-jon-jones-part-2-mma-ufc-214-daniel-cormier