From Longman Dictionary of Contemporary Englishbe out of practicebe out of practicePRACTISE/PRACTICEto have not done something for a long time, so that you are not able to do it well → practice
Examples from the Corpus
be out of practice• I'd love to play tennis with you, but I'm really out of practice.• Sam said he's a little out of practice, but he'll play if we need him. 