Can a supreme court ruling be unconstitutional

Yes

Explanation:

it has happened before in 1803 when Marbury v. Madison was the first supreme court case where the court considered it unconstitutional

yes

Explanation:

It can be although usually the constitution is taken into account when giving rulings and sentences. But yes, if the judges are not careful about what rights people actually have then can be in violation of the constitution. although rare it does happen. Their ruling cannot out weight the constitution.