The Knicks have agreed in principle on a two-year contract to sign free-agent guard Anthony Roberson, with the deal likely to expediate the departure of Stephon Marbury, The Post has learned. Knicks president Donnie Walsh appeared to be waiting to add another backcourt player before he made a move with Marbury. And now he feels he has it in Roberson, a 6-2 combo guard who is playing for the Knicks summer-league team here and excelled in his debut, scoring 22 points, including three 3-pointers.Â
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