What is a touchdown?
In the first quarter, it appeared Calvin Johnson had caught a 20-yard touchdown pass from Matthew Stafford. Upon review, officials determined Megatron didn't control the ball all the way through the process, even though he got two feet down and broke the goal line. Simply put, the Calvin Johnson rule bit Calvin Johnson once again.
To summarize the rules: A wide receiver must complete the catch after breaking the goal line for a touchdown to count, but a running back doesn't have to complete the run for it to count as a score.
It makes sense to someone.