I can't answer this any better than Sparks:
A close reading of the story will answer that question, but the answer is largely two-fold. Hegbert had a problem with the way Landon's grandfather had accumulated his wealth, and Landon himself is sort of aimless, except when he's shouting at Hegbert from behind trees. Also realize that Hegbert is secretly fearful for his daughter, and doesn't want anyone to hurt her.