The Denver Post reports Von Miller's four-game suspension is for testing positive for amphetamines and marijuana during his rookie season in 2011.
Miller entered the league with a positive marijuana test already on his resume, so the rookie-year violation was his second of the sort and necessitated a four-game ban. A third offense would knock Miller out for an entire season. Why the NFL took so long to suspend Miller is unclear, but it's believed he'll have a "hard" time winning his current appeal. The Broncos need to prepare to be without Miller until Week 5.