The Collaborative International Dictionary of English v.0.48:

Knobby \Knob"by\, a. [From Knob.]
   1. Full of, or covered with, knobs or hard protuberances.
      --Dr. H. More.
      [1913 Webster]

   2. Irregular; stubborn in particulars. [Obs.]
      [1913 Webster]

            The informers continued in a knobby kind of
            obstinacy.                            --Howell.
      [1913 Webster]

   3. Abounding in rounded hills or mountains; hilly. [U.S.]
      --Bartlett.
      [1913 Webster] knobkerrie

WordNet (r) 3.0 (2006):

knobby
    adj 1: having knobs; "had knobbly knees" [syn: knobby,
           knobbly]