When you play jazz ballads on piano, see how much you can explore the beat. Yes, it's a slow, steady pulse, but within each beat there's a whole world of rhythmic subdivisions you can tap into.
Bill Evans and his trio knew this. Listen to their famous rendition of I Loves You Porgy from The Village Vanguard and try tapping your foot on each beat.
Could you do it? It was probably tougher than you thought, huh?
This is because the trio is exploring all those rhythms in each beat that are usually not stated. You can picture each beat divided into 32 parts. Those are 32nd notes. Now, you're not going to play every 32nd note on each beat, but you might play the 4th, 15th, and 29th ones in a particular measure. Not by actually counting, but by feeling. This is what Evans and his trio are doing. They're not changing the quarter-note pulse, but they're stretching and contracting the feel within each of those beats.
Also, Evans is playing more energetic in spots than we usually think of his playing. Not just that laid-bank, mellow playing that so many pianists imitate. This relates to how he's feeling those subtle subdivisions we're listening for. The piano, bass and drums are actively engaged in a rhythmic dance, all relating to those little rhythmic possibilities that we often aren't aware of.
Listen to the recording again. Listen to it 10 times if you have time. Listen to the rhythmic interplay between the instruments as you keep time with the quarter notes. Enjoy the interplay. Then go to the piano and try it yourself.
Check out my jazz piano video course if you want improve in a step-by-step manner. I'll also give you personal guidance along the way!