The Old Legalist was one who believed that obedience to Law would gain him personal righteousness, favor with God, salvation, and heaven.
The New Legalist is held as one who believes, not in salvation by rule-keeping, but in the mere existence of rules. This is especially true if he claims the Law is external, objective, fixed.
Whereas the Old Legalist was accused of holding to Law instead of Grace, the New Legalist is accused of believing in the Law’s existence, as well as its relevance. Yet, the Bible claims the compatibility of Grace and Law:
Do we then overthrow the law by this faith? By no means! On the contrary, we uphold the law. Rom 3.31
For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them. Eph 2.10