In terms of strength, Spencers biggest problem is his legs. That is a players foundation for post defense. Most good defensive bigs have very strong legs, defend in a half-squat, and are pretty tough to back down as a result. I have noticed numerous times when Spencer gets backed down on the block, he's standing up straight, and trying to use his upper body to fend off the offensive player. That will never work.
There are a few people who want Spencer to put on 20 lbs of upper body muscle, and think that will be the difference. Thats wrong, and unrealistic. You don't defend post players with your arms. It's core strength and leg strength which helps a defender hold his position, and become a more efficent rebounder. You have to get in a half squat, and use your legs and hips to move the opponent. It has nothing to do with how much Spencer can bench press.
Spencer is playing well, and is scratching the surface of what he can potentially do as an nba center. How good will he ultimately become? Who knows. How long will it take? We have to wait and see. Personally, I don't like getting overly excited about a 2 game stretch, or getting too critical of a player for having a poor stretch. Spencer is young, the team is young. There will be many more ups and downs for this team, and Spencer. He will still hit bumps in the road, and fans will again want to get rid of him, and they will be all over Westphal for playing him too much. Funny how the opinions of some change from week to week, or even game to game.