It's hard to imagine someone surpassing Bill Russell in the number of won NBA championships anytime soon. Throughout his illustrious career, Russell established himself as a premier defensive juggernaut and the first big man that was a gifted and willing passer for his team, which was one of the reasons the Boston Celtics won 11 championships during his reign and were such a force during the '60s. However, Russell's best and most known quality on the basketball court was his defense and high basketball IQ.
Russell was the defensive anchor for the Celtics throughout all those years, and if the blocks were counted back then, there is no question he would be sitting on the top just like Wilt Chamberlain. Grabbing rebounds and blocks shots were Russell's specialty, and his reputation was so impactful that the opposing players were often hesitant to take a shot if Russell was anywhere close to them.
The psychological element of the game was a crucial one for Russell, and in an interview from 1965 under the name "How I Psych Them" he details his four main laws of basketball. All those laws played a significant role in Russell's career, and during all those years, he made sure to be at least one step ahead of the competition.
Russell's First Law: You must make the other player do what you want him to do. How? You must start him thinking. If he is thinking instead of doing, he is yours. There is no time in basketball to think: "This has happened; this is what I must do next." In the amount of time it takes to think through that semicolon, it is already too late.
Russell's Second Law: You got to have the killer instinct. If you do not have it, forget about basketball and go into social psychology or something. If you sometimes wonder if you've got it, you ain't got it. No pussycats, please. The killer instinct, by my definition, is the ability to spot—and exploit—a weakness in your opponent. There are psychological subrules in this category.
Russell's Third Law: Be cute but not cuddly. I mean, you should be nice at all times, but there is a lot to be said for an elbow in the chops when all else fails. This is forceful psychology. Last resort stuff.
Russell's Final Law: Remember that basketball is a game of habit. In getting good at it, we develop certain habits. Therefore, if you make a player deviate from his habits—by psyching him—you've got him.
These are actually pretty interesting laws that Russell lived by on the basketball court, and you can see he took his approach towards the game to another level. The majority of players don't think about the psychological aspect of the game, but Russell understood it's essential to winning games and championships. Knowing your opponent and getting into their head was Russell's primary tactic when going against the best players of his era, and it worked because all those championships are a testament to his greatness.