Luke Walton could not play in today’s scrimmage because of a sore back. He was unavailable for immediate comment after the workout because he was on the trainer’s table. Twenty-four hours earlier, Lakers coach Phil Jackson deflected questions about Walton’s play so far in training camp. He joked that Walton’s training camp was a success so far because he hadn’t come down with a nagging injury as in past Octobers. Then, lo and behold, Walton suffered a back injury after Monday’s practice. It’s unknown how long Walton might be sidelined. He played only a handful of minutes in each of the Lakers’ first two exhibitions, a win last Wednesday over Golden State and a loss Friday to the Warriors.