Hawaii Five-0 Episode 1.03 Malama Ka Aina (Respect the Land)

Danny spots a group carrying guns at a high school football game. He hustles his daughter, Grace, to safety and alerts McGarrett, who is at the game with the rest of the team (it's their alma mater). Unfortunately, a gunfight breaks out, two of the gunmen are dead, and six innocents are injured. Chin chases one of the Samoan gang members, but lets him go; turns out, he's a cousin of Chin's, Sid, who has gone into deep cover with the gang. There's been an escalating gang-war between the Triads and the Samoans and this latest attack was retaliation by the Triads for a number of recent Samoan hits. McGarrett and Danny figure out that the New Jersey mob has armed the Samoans, to provide security, so the mob can expand their gambling operations. There's a casino that night and with Sid's help, McGarrett, Danny and Kono go under cover and get evidence to stop the mob boss from moving in. The team gets their name: Five-0

Also, after the gun battle, Danny's ex-wife threatens to cut off Danny's custody rights. McGarrett gets the Governor to use her influence with the ex-wife's new husband to prevent that from happening.