Problém s dotazem

Zdravím, potřeboval bych poradit s tímto dotazem. Nevím proč, ale píše mi chybu:

#1111 - Invalid use of group function

$d = mq("SELECT
COUNT( st.id_hrace ) AS zapasy,
ty.id, ty.seo AS seo_tym, ty.nazev, ty.id_ligy,
hr.id, hr.seo AS seo_hrac, hr.id_tymu,
li.id, li.seo AS liga_seo,
st.id, st.id_hrace, SUM(st.pocet_golu) as pocet_golu, (SUM(st.pocet_golu) / COUNT( st.id_hrace )) AS prumer
FROM stat_hraci AS st
LEFT JOIN hraci AS hr ON st.id_hrace = hr.id
LEFT JOIN tymy AS ty ON hr.id_tymu = ty.id
LEFT JOIN ligy AS li ON ty.id_ligy = li.id
WHERE li.seo = '$_GET[liga]'
GROUP BY st.id_hrace
ORDER BY SUM(st.pocet_golu) DESC , prumer DESC
LIMIT 15");