The first is incorrect, the preterite of 'to see' cannot be followed by the full infinitive in this way. It ca, however, be followed by either the bare infinitive or the present participle, so 2 and 3 are both correct and mean the same thing. The speaker is referring to a time in the past when they saw him playing football at the time they saw him

Hello, My comments/suggestions are in brackets... 1: I saw him to play football [This is incorrect] 2: I saw him play football 3: I saw him playing football Both express same meaning? Both are grammatically correct? [2 and 3 are correct] Please explain their meanings [2 and 3 both mean the speaker saw him at a time in the past while he was playing football] Someone says me simple past tense doesn't use gerund or infinitive [that's true] But it can be used in this way: I told him to ask. I asked him to go. But notice here that the verbs that are in the past do not have "to" before them.