Why does chalk mean picking the favorite?

Question

why does chalk mean picking the favorite?

Answer 1

From what I heard, it comes from the horse-racing industry.  Before computers, the odds (on winning) for a horse were written on chalk boards.  

Because people tend to bet a lot on favorites, a favorite horse (and its odds) were erased and re-written a number times before the race.   Because of the changes, the name of the horse could become difficult to read.  

This lead to the term chalk.