I basically need you to send your chakra into your opponents brain, disrupting their chakra flow and suddenly make them see and feel a rope of water has suddenly materialize around them, restricting their movement and preventing them from using hand seals. Since water can easily be materialized on the battlefield, it doesn't seem anything unusual which makes it slightly useful since the opponent would have to put a good reason as to why they think it's a genjutsu, or they'd at least have to waste a jutsu so that they can prove they tried breaking the water but it doesn't break so blah blah. Of course whilst they think they're bound by a rope of water, they'd just be standing there struggling to move, since it is after all a genjutsu.