The confusion with the translation lies in this word: hypōpiazō. If we look at Strong's Concordance for this, we see the following definition:
- to beat black and blue, to smite so as to cause bruises and livid spots
- like a boxer one buffets his body, handle it roughly, discipline by hardships
- to give one intolerable annoyance
a) beat one out, wear one out
b) by entreaties
- that part of the face that is under the eyes
The first two definitions seem pretty clear that it involves beating or annoyance. The third makes me seriously question Strong's...
The Blue Letter Bible shows that that the source of this word is the conjunction of hypo with a derivitive of optanomai. These two words combined form the basis for that third definition of hypopiazo.
The definition of these two words:
hypo - "by, under"
optanomai - "to look at, behold" or "to be seen, to appear"
So the idea of the conjunction of these two concepts could be seen as being defined as "the part of the face under the eyes".
I believe that Strong's adds that third definition of the word purely based on the etymology. If we keep in mind the fact that this is a verb, we see that "the part of the face that is under the eyes" doesn't really do anything. If this third translation was related to some other part of our body that had action (mouth, legs, feet, lips, eyelids, hair, etc.) I can see that the definition could be that. However, with the etymology being an area that has no action and cannot take part in action, I feel that the third definition is probably not useful for this.
So we see the passage:
αλλ' υπωπιάζω μου το σώμα
[But] [?????] [My] [... body]
What is Paul doing to his body? Is it something to do with the part of the face under his eyes? I doubt it.
I think we can be confident in the translation of "bruise". We could even be confident of the translation "beat" or "beat black and blue" in this sense. The translation "discipline" is more of a loose translation than "bruise". In this sense "bruise" is the literal translation.
See Translation Philosophy of the English Standard Version for more information.
The literal, word-for-word translation from Greek would be:
"But [I beat-black-and-blue] my body"
Although that word has roots that mean "under the eye", it is a verb and should be understood based on the word definition, which is "to bruise" or "to beat black and blue", rather than the source of the word, which would be "under the eyes".