a day devoted to outdoor sports or athletic contests, as at a school.
2.
an outdoor gathering; outing; picnic.
3.
a day for military exercises and display.
4.
an occasion or opportunity for unrestricted activity, amusement, etc.:
The children had a field day with their new skateboards.
Origin
1740-50
Examples from the web for field day
No wonder the anti-science majority have such a field day shooting us down.
Every predator in the area would have an immediate field day.
In this scenario moralists and reformers would have a field day.
Our partisan politicians must refrain from taking sides and making a field day out of unfinished science.
Another couple of years of this and we're looking at a field day for corporate bankruptcy lawyers.
The report was immediately leaked for money to the tabloids, and the media had a field day.
If the press found out, they would have a field day with it.
However, there is a negative side to everything and as mentioned in the article criminals could have a field day.
And, the lawyers are going to have a field day with that one should the security of an application be seriously compromised.
Local papers had a field day with these and other signs spotted by the visitors.
British Dictionary definitions for field day
field day
noun
1.
a day spent in some special outdoor activity, such as nature study or sport
2.
a day-long competition between amateur radio operators using battery or generator power, the aim being to make the most contacts with other operators around the world
3.
(military) a day devoted to manoeuvres or exercises, esp before an audience
4.
(informal) a day or time of exciting or successful activity: the children had a field day with their new toys
5.
(Austral)
a day or series of days devoted to the demonstration of farm machinery in country centres
a combined open day and sale on a stud property
Word Origin and History for field day
n.
1747, originally a day of military exercise and review (see field (v.)); figurative sense is from 1827.
A time of great pleasure, activity, or opportunity, as in The press had a field day with this sensational murder trial. This colloquial expression, dating from the 1700s, originally referred to a day set aside for military maneuvers and exercises, and later was extended to a similar day for sports and games. Since the early 1800s it has been used more loosely.