not as good as it used to be, because you have not been practising 荒疏；荒废；退步
My tennis is very rusty these days.
最近我的网球荒疏了。
I haven’t played the piano for ages—I may be a little rusty.
我很久没有弹钢琴，可能会有点生疏。
covered with rust 生锈的
rusty metal
生锈的金属
a rusty old car
生了锈的旧汽车