I added display: block;
now span works.
https://jsfiddle.net/ueL42ym3/1/
.circle {
display: block;
}
<button class="playa thePlay">
<span class="circle"> <svg class="play" width="38" height="22" viewBox="0 0 26 26">
<g id="play">
<title>Play</title>
<path d="M7.712 22.04a.732.732 0 0 1-.806.007.767.767 0 0 1-.406-.703V4.656c0-.31.135-.544.406-.703.271-.16.54-.157.806.006l14.458 8.332c.266.163.4.4.4.709 0 .31-.134.546-.4.71L7.712 22.04z" fill-rule="evenodd" />
</g>
</svg> </span>
</button>