首先，你的HTML无效，因为你的第二个HTML无效form，嵌套在第一个中，没有结束标记。同样，虽然不关闭p元素是合法的，但为清楚起见，你确实应该这样做。
接下来，从HTML中删除内联样式和内联JavaScript。它只会使代码混乱，导致冗余，并且难以阅读和维护。而是将你的工作分为HTML，CSS和JavaScript部分。
目前尚不清楚你到底想要什么，但是我的猜测是，无论单击哪个单选按钮，都应该决定哪个文本框值成为赢家。基于此，请参见下面的内联注释，以获取有关代码工作方式的描述。
.autocomplete { width:300px; }<!--Make sure the form has the autocomplete function switched off:-->
<form autocomplete="off" action="/action_page.php">
<div class="courses">
<div class="autocomplete">
Course 1 <input id="myInput" name="golfcoursename1" placeholder="Golf Course">
</div>
<div class="autocomplete">
Course 2 <input id="myInput1" name="golfcoursename2" placeholder="Golf Course">
</div>
</div>
<p>WINNER</p>
<p id="radioContainer">
<input type="radio" id="Course1" name="winnerselected" value="Course1">
<label for="Course1">Course 1</label>
<input type="radio" id="Course2" name="winnerselected" value="Course2">
<label for="Course2">Course 2</label><br>
<input type="text" id="winner" name="Winner" placeholder="Winner">
</p>
<input type="submit">
</form>
<script>
// Don't use inline HTML event attributes like onclick.
// Separate your JavaScript from your HTML
// Get references to the element(s) you'll need to work with
// Get all the elements that have a name attribute that starts with "golfcoursename"
const courseNames = document.querySelectorAll("[name^='golfcoursename']");
// Get all the elements that have a name attribute that is exactly "winnerselected"
const radioButtons = document.querySelectorAll("[name='winnerselected']");
const winner = document.getElementById("winner");
// Here's how to set up events in JS
const radCont = document.getElementById("radioContainer").addEventListener("click", fillWinner);
function fillWinner(event) {
// Look at the radiobuttons collection and get the index of the selected radio button from it.
const indexOfTextbox = Array.from(radioButtons).indexOf(event.target);
// Set the value of the winner textbox to textbox with the same index as the clicked radio button
winner.value = courseNames[indexOfTextbox].value;
}
</script>