When writing these report cards, players are evaluated a few different factors each comprising their own sort of curve, which are all then weighed to the tastes of the writer reviewing the player’s season. These factors include grading the player’s season relative to the rest of the league, their personal expectations (preseason projections), and the role the team expected the player to fill.
Personally, I tend to weigh the latter two factors fairly heavily, which leaves me at something of a loss when evaluating Tommy Joseph. He was the headline piece of the Hunter Pence trade to San Francisco back at the 2012 Trade Deadline.