I moved your question to general criminal defense so you may get additional responses. It is perfectly legal for a person to be arrested via warrant. It also COULD mean the case is serious as law enforcement, perhaps in consultation with the State Attorney's office. Additionally, due to the coronavirus virus, with few exceptions, the courts are closed. Look to hire an attorney now who can perhaps quickly move this case along. Good luck!

Yes, it is perfectly legal to be arrested on a warrant. Many cases, from those in Federal court to felony cases in State courts, are initiated by an arrest. There may be other legal issues that he can explore in his defense regarding the legality of the investigation, but being arrested on a warrant is usually not something that is successfully challenged. I suggest you seek the counsel of several experienced criminal defense lawyers, meet with 2-3 in person and hire the best one for your grandson's circumstances.

Being picked up on the warrant was his arrest.

The warrant was issued after being reviewed by a Judge who determined that it contained probable cause to believe that your grandson committed a crime and once issued and served the arrest for that crime was effectuated.

It is now time to lawyer up and let a skilled and trained professional review the affidavit in support of the warrant, levy any challenges that may exist and otherwise begin to prepare a meaningful and effective defense.

Wishing your grandson luck and hoping that I have been helpful in answering your question.