Sportsmen greeting one another with a bow

It is not permissible to bow to anyone when greeting them,
whether in the context of sports or otherwise. The Prophet (blessings and
peace of Allaah be upon him) forbade that. 

Al-Tirmidhi (2728) narrated that Anas ibn Maalik (may Allaah
be pleased with him) said: A man said: O Messenger of Allaah, when one of us
meets his brother or friend, should he bow to him? He said: “No.” He said:
Should he embrace him and kiss him? He said: “No.” He said: Should he shake
hands with him? He said: “Yes.” Classed as hasan by al-Albaani in Saheeh
al-Tirmidhi. 

Al-Mubaarakfoori said in Tuhfat al-Ahwadhi: 

Bowing means tilting or inclining the head and back. 

“He said: ‘No’” because it is the same as rukoo’ (bowing),
which like sujood (prostration) is an act of worship before Allaah, may He
be glorified. 

“Should he embrace him” i.e., hug him and clasp him to
himself, “and kiss him. He said: ‘No.’” End quote. 

The scholars of the Standing Committee for Issuing Fatwas
were asked: We joined a karate club in America and the trainer said that you
have to bow when he bows to you. We refused and explained to him that this
is against our religion, and he accepted that but he said that we should
tilt our heads only, because he is the one who bows first and it is
essential to return his greeting.  What is your opinion on that? 

They replied: It is not permissible to bow in greeting to a
Muslim or to a kaafir, whether that involves the upper part of the body or
the head, because bowing is a kind of worship, and worship is only for
Allaah alone. 

And Allaah is the source of strength. May Allaah sent
blessings and peace upon our Prophet Muhammad and his family and
Companions. 

Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah ibn Baaz, Shaykh ‘Abd al-Razzaaq ‘Afeefu, Shaykh ‘Abd-Allaah ibn Ghadyaan, Shaykh ‘Abd-Allaah ibn Qa’ood