I read this article which gave a little insight into Brown's play at Cal. https://www.reddit.com/r/bostonceltics/comments/4q2s2j/translation_an_interview_with_a_data_analyst/
One interesting take away is that it pointed out why he played poorly at the end of the season. In a game at Arizona on March 3rd, Brown was called for 3 offensive fouls when trying to drive to the hoop and fouled out of the game. Some argued that Arizona was flopping and Brown got a bad break. After that game, he was very tentative on the offensive end which led to his poor performance. Those games included the conference and NCAA tournament which is when a lot of people were watching and therefore have a bad impression of him. Prior to that he had been on a roll. It's not an excuse, but it is an understandable reason especially for a freshman.
If you look at his game log, you'll see that game was the start of his poor play. http://www.sports-reference.com/cbb/players/jaylen-brown-1/gamelog/
Lol, way to learn from your mistakes (sarcasm)
. GP II locked him up two games after this one against Arizona, despite giving away 4 inches and 50 lbs
. He also 'chipped in' 20 points on 7-15 fg, 1/3 3pt, and 5/7 ft to go along with 17 rebounds
, 2 assists, 2 steals, 2 blocks, 5 turnovers, and 3 fouls. Holy crap. What a player, and a two way one, at that. How on earth did he go undrafted? Unbelievable.