What is the test for a federal court to rule on an interpretation of state law by a state court?

An important corollary to the above is that federal courts may not rule on state law issues, and are bound by state court interpretations of those issues unless the state interpretation is so strained that it becomes simply a subterfuge to avoid the federal issue that is otherwise plain to see. Butler v. Curry, 528 F.3d 624, 642 (9th Cir. 2008). A federal court must examine this exception de novo as there will be no state decision acknowledging an arbitrary determination on state law for the purposeful avoidance of federal law.

B. The "Counsel" Claim Involves Only an Interpretation of State Law