It’s hard to tell where to begin with Kevin Garnett. The Celtics center suffered a hip pointer Tuesday night, according to coach Doc Rivers, though Garnett is expected to practice today and play Friday night in Game 3 against the New York Knicks at the Garden. “It affected him, and I kept asking him if he was OK (Tuesday night), but he’s good,” Rivers said during a conference call yesterday. “It won’t keep him out.” Instead, factors other than injuries have kept Garnett out of meaningful action in this series. Overall offensive dysfunction kept him from getting established during the Game 1 loss Saturday, and foul trouble limited him to 24 minutes Tuesday night in Game 2. The Celtics can’t afford another night without their center at full strength, physically and mentally. “Him getting in foul trouble had a huge impact on the game,” Rivers said. “I actually thought he started out great, and then the fouls started. He was never allowed to get his rhythm going.” Thus far, Garnett simply can’t win. But Rivers, who still was angry about the nature of the early calls that sent Garnett to the bench, admits the Celtics have to do a much better job protecting the core of their defense. That means cutting down on the Knicks’ dribble penetration, especially by Raymond Felton, and sparing Garnett unwanted matchups. That’s where he fell into trouble Tuesday night. “You’ve got to keep guards out of the paint,” Rivers said. “He picked up the first foul guarding (Carmelo Anthony). We have to protect him, clearly, and we have to keep him out of bad matchups.” And Rivers admittedly has to be careful about what he says about the officiating, even though he feels the need to advocate for his players. “I can’t say anything,” Rivers said. “Even (Tuesday night) I didn’t say much, and that was a problem. But there’s nothing I can do about it. At the end of the day, we got outplayed in the effort department and the desperation department. The Knicks played like their season was on the line.”