Be/get out of practice
Definition 1 of 1
Pro Tip 1/3Regular Practice
Frequent activity keeps skills sharp; infrequent activity leads to the phrase 'out of practice'. 
If you don't practice speaking English, you might soon find yourself out of practice.
Pro Tip 2/3Skill Decay
When a skill isn't used often, it can fade away, like muscles can weaken without exercise. 
I'm out of practice at biking; hills are much harder now.
Pro Tip 3/3Temporal Reference
The phrase often implies that there was a time when the skill was better due to regular use. 
She was out of practice with her French since she hadn't visited France in years.