The Geat's efforts to help Beowulf turns useless because Grendel, the monster was able to kill the Geats before reaching to Beowulf.
Beowulf alone killed him by gripping his hand.
Explanation
Grendel was strong and voracious.
He had no mercy and killed people continuously.
He continuously attacked the Kingdom of Danes which was ruled by King Hrothgar since the king threw the feast to his people.
His men were not able to defeat Grendel.
This news was spread to the tribe of Geats where Beowulf was a member.
So, he decided to attack Grendel and came with some of his people.