There certainly are more obvious differences between these two characters. Matt is older, married and with three children, and he is the character that all the emotions of his family seem to be expressed towards after Frank's murder. He enjoys a very close relationship with his wife, Ruth, and therefore the pain that Ruth experiences at seeing her son's murderer walking around is something that Matt experiences too. Matt is a character who is defined by responsibility, and his son's death has made him review his success as a parent and his ability to keep his son safe. It is the pressure and stress of losing his son in such a way and facing his son's murder that transforms this gentle and sensitive character into somebody willing to commit a murder.
Richard on the other hand is not successful and does not enjoy a close relationship. Although he did enjoy some success thanks to this sporting prowess, this was short-lived, and he ended up working as a bartender whilst being supported by his father. Richard is a character who is not respected and he has a number of enemies.
The one similarity that I can identify between them is that both commit murder because of an unbearable situation, though this is more tenuous with Richard. On the one hand, Richard saw Frank as a barrier in the way of restoring his relationship with Mary Ann. On the other hand, the way in which he did this while drunk indicates that this was not premeditated.