When you seize an opportunity, you take advantage of it and do something that you want to do. During the riots hundreds of people seized the opportunity to steal property
If you seize something, you take hold of it quickly, firmly, and forcefully. `Leigh,' he said seizing my arm to hold me back. an otter seizing a fish
vt to put in legal possession of a prticular thing; assign ownership to (in the passive voice)
{f} take forcibly; grasp, hold; comprehend, understand; expropriate, confiscate; capture, apprehend; take control of; take advantage of promptly; attack; (Law) make a person the legal owner of merchandise or property; lash, tie or fasten something using several turns with a rope or cord
capture the attention or imagination of; "This story will grab you"; "The movie seized my imagination"
take hold of; grab; "The salesclerk quickly seized the money on the counter"; "She clutched her purse"; "The mother seized her child by the arm"; "Birds of prey often seize small mammals"