When scissors denotes a cutting implement, it can be either plural or singular. For example, both hand me those scissors and hand me that scissors work. Many usage authorities recommend treating scissors as plural, however, and doing so may be the safer choice. When you need it to be singular, pair of scissors is a good alternative.
Writers sometimes change scissors into scissor when it’s singular, but there’s no need for this. Scissor does work as a verb—meaning to cut or clip with scissors—but it’s not a dictionary-recognized noun. Again, scissors can be treated as singular.
But in sports, where scissors is a gymnastic exercise and a wrestling hold, there is no question about it: Scissors is singular.