Observations for immediate improvement...and lowering my blood pressure.
First, timing and execution on screening. Way too many illegal screen calls or ineffective screens. From not getting there on time to the player with the ball moving before the screen is set or even not getting the angle of the screen correct - you name it, Cal's done it....
Second, not being aware of where the ball is in relation to the player you're guarding. Cal has too many players not knowing where the ball is...a lot of times, their head is turned and that's an invitation for the pass to be made. If you don't know where the ball is, how can you defend effectively? Plus, how do you know when or if you need to help if you can't see the play?
The first needs to be addressed in practice? The second can be shown on film, but to me it's putting yourself in a better position to keep track of where the ball is and keeping in contact with the player you're guarding. Mental awareness and effort.
There are some good players here and we don't lose any rotation players to graduation. So there is a bright side if everyone commits to making improvements.
Opinion: Cal needs to push tempo.
Last point: if Cal played the entire 40 minutes with the grit, effort and determination as they did in the final few minutes of this game, they'll be okay. If they improve on their defensive awareness and offensive execution, they can be very good.