In the offseason, Spider Jerusalem of Golden State of Mind analyzed both Ellis and Curry when it wasn't clear whether both would be returning (click through to find out more about their offensive numbers and get all the statistical tables in one place, which are also very interesting!).
Analysis: Quite promising numbers for the Golden Babyfaced Assassin Child. Intuitively, I felt like he had good defensive fundamentals, and understood how to stay in front of his man well enough, and Synergy backs that up somewhat. Being strong against the main attack modes he'll see his entire career as a rookie is an encouraging sign. Bigger guards will always try to post him up, but aside from the high shooting foul percentage, he's able to take care of himself, and can defend the Isolation/P&R better than a lot of veteran PGs already. Amazing. Big time struggles in the rotation department, and that shows up in Spot-Up defense. Some of that will be team defense, but a lot of that is Curry needing to learn NBA rotations. Rookies are expected to struggle in that area, and Curry is a rookie. Even if he stealth kills babies with his golden face.
Again, Monta comes out not looking so good. He's below average to downright terrible in every single category. Even excusing the Spot-Up numbers due to team defense, there are too many deficiencies to overlook. Combined with his average-at-best offense and Synergy paints a pretty damning picture of Monta. So, he's on a moped, obviously.
With the departure of Don Nelson and the arrival of Keith Smart, the Warriors seem to have focused more on defense, and the tables have turned defensively. Matt Steinmetz at Comcast Sports Net Bay Area has more on why Ellis can be such an effective defender.
So why has Ellis become such an efficient defender after lacking that ability last season? Perhaps it was psychological; Ellis was probably languishing from Nelson's notorious head games, and seemed to be ready to demand a trade if Nelson returned. In any case, Smart seems to be pushing the right buttons with Ellis, and hopefully when he returns he can move forward with his defensive progression.
The question will be consistency. Even Steinmetz doesn't know how long Ellis will keep it up. He's going to need more help.