Grabbing the collar from behind with one hand
Bear hug from behind (squeezing the chest with both arms)
Choking hold from behind where UKE's other hand fixates TORI's hand.
Grabbing both ellbows from behind
Grabbing both shoulders from behind
Uke grabs both of tori's wrists from behind. This attack is usually practised dynamically, starting from the front with contact of one hand. It is also known as ushiro-tekubi-dori.
A comprehensive collection of instructive videos is available under Media > Basic Forms.