Out of practice
Meaning: to not do something well because you have not done it recently, performing poorly due to a lack of practice (*Typically: be ~; get ~; go ~)
Example: I used to be able to play the piano extremely well, but now I'm out of practice. The baseball players lost the game because they were out of practice.
Example: I used to be able to play the piano extremely well, but now I'm out of practice. The baseball players lost the game because they were out of practice.