Yards per attempt
No one metric is even remotely close to perfect for evaluating quarterback play, but plain-old Y/A (yards per attempt) is one of the more solid passing metrics out there.
Darnold averaged 6.9 Y/A in each of his first two seasons, placing him 26th of 33 in 2018 and 23rd of 32 in 2019.
I would like to see Darnold push into the top 10-15 range of Y/A. In 2019, this range spanned from 10th-ranked Drew Brees (7.9) to 15th-ranked Matt Ryan (7.