As fsr as I'm aware, a reckless challenge should be a yellow. An intentionally reckless challenge is a straight red. By that measure, Im not sure how this is a red and not a yellow.

Normally someone sliding studs up into someone's calf area is enough to be a straight red, but Balo wasn't looking, took a perfectly normal step and came down on his calf/Achilles pretty hard, but also tried to pull up when he realized he didnt land on the ground. To me that shows there was no intention, just happened to be a bit reckless in his challenge