Interestingly, the HC expounds the fourth commandment as follows:
Question 103. What does God require in the fourth commandment?
Answer: First, that the ministry of the gospel and the schools be maintained; (a) and that I, especially on the sabbath, that is, on the day of rest, diligently frequent the church of God, (b) to hear his word, (c) to use the sacraments, (d) publicly to call upon the Lord, (e) and contribute to the relief of the poor. (f) Secondly, that all the days of my life I cease from my evil works, and yield myself to the Lord, to work by his Holy Spirit in me: and thus begin in this life the eternal sabbath. (g)
While the WCF approaches the fourth commandment from a slightly different angle:
VIII. This Sabbath is to be kept holy unto the Lord when men, after a due preparing of their hearts, and ordering of their common affairs beforehand, do not only observe an holy rest all the day from their own works, words, and thoughts about their worldly employments and recreations; but also are taken up the whole time in the public and private exercises of his worship, and in the duties of necessity and mercy.
If you have read Calvin's Institutes, you will observe that the HC basically summarizes Calvin's teachings on the Lord's Day, while the WCF contains more of a Puritan perspective on the fourth commandment, such as mention that recreation must cease. I personally agree with both views, but I know that some Reformed folks at my church do engage in some recreation on the Lord's Day, such as our young adults group playing football together in the field after the evening service (occasionally in the summer). I think we consider that one OK because we are spending time together.