I run cross-country and play soccer, unfortunately our training and ramadan coincide heavily this year. Should I fast? or should I not fast on the days I have practice/meets/games? And what are the rules for making those days up?
Rules of fasting are well described Quran, in these Ayas:
يا أَيُّهَا الَّذِينَ آمَنُوا كُتِبَ عَلَيْكُمُ الصِّيَامُ كَمَا كُتِبَ عَلَى الَّذِينَ مِن قَبْلِكُمْ لَعَلَّكُمْ تَتَّقُونَ
O you who have believed, decreed upon you is fasting as it was decreed upon those before you that you may become righteous -
أَيَّامًا مَّعْدُودَاتٍ ۚ فَمَن كَانَ مِنكُم مَّرِيضًا أَوْ عَلَىٰ سَفَرٍ فَعِدَّةٌ مِّنْ أَيَّامٍ أُخَرَ ۚ وَعَلَى الَّذِينَ يُطِيقُونَهُ فِدْيَةٌ طَعَامُ مِسْكِينٍ ۖ فَمَن تَطَوَّعَ خَيْرًا فَهُوَ خَيْرٌ لَّهُ ۚ وَأَن تَصُومُوا خَيْرٌ لَّكُمْ ۖ إِن كُنتُمْ تَعْلَمُونَ
[Fasting for] a limited number of days. So whoever among you is ill or on a journey [during them] - then an equal number of days [are to be made up]. And upon those who are able [to fast, but with hardship] - a ransom [as substitute] of feeding a poor person [each day]. And whoever volunteers excess - it is better for him. But to fast is best for you, if you only knew.
شَهْرُ رَمَضَانَ الَّذِي أُنزِلَ فِيهِ الْقُرْآنُ هُدًى لِّلنَّاسِ وَبَيِّنَاتٍ مِّنَ الْهُدَىٰ وَالْفُرْقَانِ ۚ فَمَن شَهِدَ مِنكُمُ الشَّهْرَ فَلْيَصُمْهُ ۖ وَمَن كَانَ مَرِيضًا أَوْ عَلَىٰ سَفَرٍ فَعِدَّةٌ مِّنْ أَيَّامٍ أُخَرَ ۗ يُرِيدُ اللَّهُ بِكُمُ الْيُسْرَ وَلَا يُرِيدُ بِكُمُ الْعُسْرَ وَلِتُكْمِلُوا الْعِدَّةَ وَلِتُكَبِّرُوا اللَّهَ عَلَىٰ مَا هَدَاكُمْ وَلَعَلَّكُمْ تَشْكُرُونَ
The month of Ramadhan [is that] in which was revealed the Qur'an, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the new moon of] the month, let him fast it; and whoever is ill or on a journey - then an equal number of other days. Allah intends for you ease and does not intend for you hardship and [wants] for you to complete the period and to glorify Allah for that [to] which He has guided you; and perhaps you will be grateful.
So If you are travelling, then you are allowed not to fast the days you are travelling, but must fast them (same number of days but not necessarily continuously) after Ramadan (and before the next Ramadan, needs citation).
However, if you are talking about being allowed not to fast because you play sport (hard work), then it's not allowed, as it wasn't mentioned in Quran that hard works permit not fasting, in truth it was said in the Ayas quoted up there that even if you are allowed not to fast, it's better if you do.
However, among those allowed not to fast are the sick. And, from this, the majority of Shafi'i, Hanafi, Maliki, and Hanbali scientists said it's allowed not to fast (and fast the same number of days after Ramadan and before the next Ramadan) if you were working necessary extremely hard work that could lead you to illness or doom. And this is reasonable: one purpose of fasting is to restore healthiness, not be lose it!
I, for one, advice you against it, no matter how hard the sport you play, it's not as hard as the work Muslims did in Jihad. They were allowed to skip fasting (since they were travelling), but they didn't, so head their way and God will grant you power and help you Inshallah :)
Ramadan is a month which we spare for fasting. Fasting in that month is fard. When an ibadat is fard, it is obligatory. Allah's orders are above anything, and must be done no matter what. All actions that would prevent us from fasting are canceled in that month. There is no exception for this (only exceptions are those mentioned in suratul Bakara; you can find them in other answers). We do long term plans for physical activities (like vocation, diet, work, traveling, etc) considering the Ramadan month.