Defrost shrimp and dry well. Carefully push one rosemary sprig through each shrimp.
Combine the olive oil and garlic.
Brush shrimp with the olive oil and garlic mixture and let rest in the refrigerator for an hour or so.
Heat a grill, griddle, or heavy-bottomed pan and cook the shrimp just until they change color, about 1-1½ minutes on each side. Serve immediately.