<?php $i = 1; ?>
<div class="row">
<?php while ( have_rows('unite') ): the_row(); ?>
<div class="col-md-3">
<h3><?php the_sub_field('nom'); ?></h3>
</div>
<?php
if( $i == 4 ){
echo '</div><div class="row">';
$i = 0;
}
$i++;
?>
<?php endwhile; ?>
</div>