SpellsCurse
Locomotor Mortis
The Leg-Locker Curse locks a person's legs together. Draco uses it on Neville in Philosopher's Stone; Hermione lifts the curse when Neville reaches the common room.
In the books
Harry Potter and the Philosopher's StoneChapter: 13
Draco locks Neville’s legs together, and Hermione frees him with a counter-curse.