@keyframes play {
    from { 
        background-position: 0px; 
    }
    to { 
        background-position: -800px; 
    }
}
    #walk {
        margin: auto;
        width: 200px;
        height: 400px;
        background-image: url("../img/ninjasprite.png");
        animation: play 0.5s steps(4) infinite; /* new line */
    }
   
    #court {
        position: relative;
        overflow: hidden;
        margin: auto;
        width: 900px; height: 900px;
        background: #eee;
        border: solid black 2px;
      }
      #ninja {
        position: absolute;
        width: 506px; height: 593px;
        border-radius: 50%;
        background-image: url("../img/ninjajump.png");
      }

    #grey {
        width: 500px
    }