Jumpers for goalposts means: Informal association football as played by children, especially as a romantic or old-fashioned ideal contrasted against the commercialism and cynicism of modern professional football.. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. It is sporting vocabulary and harmless in itself. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.