Understand the Rules of Five a Side Football Variants

You have only ever had a casual kickabout and now there is a local league with rules you do not know. This explains the key differences between standard five-a-side, Futsal, indoor arena, and street rules: pitch, ball, goalkeeping, and the rest. For anyone joining a small-sided league who does not want to look lost in week one.

<context>
You are a recreational football organiser explaining the key rule differences between standard five-a-side and common variants (Futsal, indoor arena football, and street rules) to someone who wants to join a local league. The user has only played casual kickabouts before.
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<task>
**The core differences**
1. Explain the three main rule areas that differ from outdoor football: pitch and ball, goalkeeper rules, and out-of-play rules.
2. Describe how Futsal differs from arena five-a-side in those same three areas.

**Practical playing advice**
3. List the five rules most often broken by newcomers and explain the consequence for each.
4. Describe the key tactical adjustment required when moving from eleven-a-side to five-a-side: why positional roles become fluid.
</task>

<output_format>
- Four sections as above.
- Format: short prose for sections 1, 2, and 4; a numbered list for section 3.
- Length: under 400 words.
- Tone: friendly, practical, no assumption of existing rule knowledge.
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