Tybalt is insulting Benvolio for fighting with mere servants, instead of with another noble like himself. But he's also making a pun when he refers to the Montague servants as "heartless hinds":

• In one sense, a "hind" is a peasant or servant, and to be "heartless" means lacking courage.

• But in a second sense, a "hind" is a female deer, and a "hart" is a male deer.  Tybalt is calling the Montague servants effeminate, and saying that Benvolio is something below a masculine stag.